General Diagnosis of Problems with Your Imperial's Carburetor


Imperial Homepage -> Repair -> Fuel -> Carburetor -> Diagnosis

Tip from Dick:

If you want to see if your carburetor is working OK but don't want to run gas through your fuel lines or in your tank, you can safely dribble a few ounces of fuel into the bowl vents that come out the top of the carburetor, this will fill the float bowls and allow the engine to run even if the fuel pump/lines/filter/tank system is not working. Replace the air cleaner after you put the gas in the carburetor, to prevent a flashback of fire in case an intake valve is stuck open. If it does start for a second and then dies, you can add more gas to the carburetor by trickling it down the center screw under the wingnut on the air cleaner, without removing the air cleaner. If you do experience a flashback through the carburetor, keep cranking to suck the flames back into the engine. It won't hurt the engine, but flames will sure mess up your hood (and your eyebrows!).

Question from Luke:

New engine starts first time but if I try to start it again she's flooded and I have to wait half a day to start her again. Is anyone real familiar with the Carter carburetor? I'm going to consult the manual but if anyone has been here before I would appreciate any tips.  

Reply from Dick:

A new engine and flooding are a very bad combination, because the excess fuel is going to wash the lubrication off the cylinder walls and possibly cause some severe damage... Regardless of the cause of the flooding, don't keep repeating this situation. In fact, if the car has liquid gas in the intake now, don't crank the engine at all. Remove the spark plugs and put motor oil in each cylinder, then with the plugs still out, crank the engine a few times to wet the cylinder walls with oil. Before you do this, remove the carburetor to prevent any further flooding.

The carburetor problem is likely to be a stuck float valve, or a float that doesn't. Take the top off the carburetor and investigate. If the float chambers are full of gas, see if you can blow into the fuel inlet. If you can, one of those things is your problem. If you can't, the float valve is closed now, but it may be sticky or not sealing perfectly. You'll just have to figure it out yourself or get a carburetor guy to check it out for you.  This is a very reliable carburetor, not known for problems, so an errant piece of crud is a likely explanation, especially since the engine has been all apart.

Question from Zeke:

I am having a terrible flooding/not starting up in the morning problem with the carburetor. The carburetor was rebuilt and still does not work well. The problem I am experiencing is...I cannot find a replacement.


From Norm:

Check for correct operation of the choke pull off. Your carb probably has one ( all AFB's have one- I imagine yours will , too) . What it does is crack the choke plate the minute the engine starts so that it will run on a rich mixture, but not so rich that it will flood and not run.

From Pete:

Do you have a Holley 4160? Remove the air cleaner and look at the front edge of the air horn (the flat vertical area ahead of the choke plate). You should see a number like "R-4366" and then 2526 or something like that. What are the numbers? I'd expect a 67 to have the Carter AFB. What say you other '67 owners? If you DO have a Holley 4160 I can probably help you since I had to tear the one in my 70 apart about 10 times before I found the problem that was causing such grief. I can now field strip and reassemble one of these while asleep. If you care to ship yours to me I can probably solve your problem. These carbs are not terribly complex but they do have some quirky areas that you need to check carefully during the rebuild process. As for finding a good used carb (Carter or Holley), that will be difficult (as you already know) and you never know what's been done to one when you do find it. Holley does make a Mopar replacement 4160 (#80454) but it is available in only electric or manual choke versions. Also, the fuel inlet pipe is routed differently. Carter also offers replacement carburetors. Expect to pay $200-$300.

Question from Ted (1955):

I have never had a hard start with a 12 volt Chrysler engine but often have with my six volt '55 Hemi. I have found that making sure the connections are dry and tight helps, but believe there is a heat soak vapor lock problem also. The engine turns slower when hot, which might indicate cylinders full of gas vapor. Some of this gas may leak down into the cylinders while the engine is off. I have thought of a six volt electric pump, but feel since the car started fine when new, I shouldn't need it if everything is right.

Does any other six volt Imp owner have this problem? Has anyone replaced the manifold to carb gasket to solve it? Who sells the gaskets?? Is this a good idea or am I looking at a carb rebuild? Like Jason's, mine starts well when cold.


From Roger:

Jeff Carter is selling new Carter fuel filter elements and they come with a new gasket for the filter bowl.

JC Auto Restoration, Inc.
20815 52nd Ave W #2
Lynnwood, WA 98036
Tel: (425) 672-8324
Fax: (425) 771-2522

From Kerry:

If your hard starting when hot is indeed caused by fuel vapor it is PROBABLY caused by fuel expanding in the carb bowl when the carb soaks the engine heat after you stop. The fuel can expand and overflow the bowl and run down into the engine flooding it. Lowering the fuel level by adjusting the float can solve this and has on several of my Mopars including a 54, 64, and two 73's.

From John:

I've seen this problem before. One car I remember was a co workers '68 Dodge Monaco Wagon that would do that. I would describe it more as hard cranking then hard starting.. Occasionally when trying to start hot, it would slooowly crank until the battery seemed about dead. Letting the car cool for 15-20 minutes & it would start right up again.

Question from Gerry (1956):

I just got my '56 Imperial home from the shop today after an extensive restoration. It was there for almost 2 years. However there are some minor glitches that I need help with. At the left side and slightly to the rear of the carb (assuming you are sitting in the driver's seat looking forward) is an assembly composed of a rubber diaphram, spring, idle set screw, and the main throttle linkage from the foot pedal passing through and attached to the right side of this assembly. What the heck is this doo hickey called? What is the impact if the rubber diaphram is cracked? It is cracked and you can easily see the spring just underneath. I can't see any vacuum lines running into this unit. In any case I am having trouble getting the engine to go to a slow idle even with the idle set screw backed right off. The return spring is plenty strong enough. Engine was completely overhauled along with the carb however the unit I am refering is not attached directly to the carb so was not overhauled.

Reply from Brad:

I have both a '55 coupe and '56 limo both with A/C and noticed that this dashpot is there, along with an electronic/pneumatic solenoid that is forward of it. The two items seem to work together. On the A/C cars the shop manual says that the electronic /pneumatic solenoid is meant to raise the engine idle when the A/C is on and the engine is in neutral (sounds like your situation ???) presumably so the engine will not stall with the A/C engaged. I looked at the '56 shop manual and the only mention of a solenoid was in the A/C section in the electrical schematic. The 1955 shop manual has quite a bit more information in the A/C section including an adjustment procedure for the electro/pneumatic solenoid. My thought on the dashpot (passive element) is that perhaps it is used in the system to gradually lower the idle when the system is in operation. This is just an opinion since there is nothing about itís impact to the system.

Does your car have A/C?

Follow-up from Gerry:

My '56 does not have A/C. I think I have figured it out. The unit in question seems to be related to the shifting and kick-down speeds. The main throttle linkage goes through a slider with an ajustment nut to lock it in place. I have it just right and shifting very smoothly now. I found the reason for the high idle even with the set screws backed off. There is a spring on the throttle shaft which runs through the base of the carb. This spring is on the bottom right side of the carb and was installed incorrectly so that there was no return tension to the shaft. Got it idling very nicely now.

Question from Philippe (1957):

I am having a problem with my Imperial.  Here is the car's resume: 

engine: 392 hemi (stock) 

carb: carter WCFB 2590S 4 bbl (stock and rebuilt) 

ignition: (stock)

vacuum chamber: not leaking but 40 years old! 

no "power package" or "exotic cam & ignition"... 

ignition tune: 7 to 8 0 BDC (with vacuum line removed and plugged) 

idle set at 600 rpm (couldn't go lower... if I try, the idle screw doesn't contact any longer the idle stop lever..). 

Now my problem...At 600 rpm if I measure the amount of vacuum in the vacuum line (this line comes from a port in the carburetor base, near the idle mixture screws), the vacuum meter reads 12 inch / hg. I would have less 'cause I think it's a "timed port ": it's the only vacuum port in the carb (I don't speak of intake manifold port) and the tube from vacuum chamber to port have the correct bending to go here... If I run the engine faster (1000rpm or more) the vacuum increases to 14 inch / hg. If I open wide, the vacuum drops then increases again to 12 to 14 inch /hg.  So in fact, the vacuum is between 12 & 14 except in wide open situation. Is there something wrong with the carburetor?  An internal carburetor vacuum line plugged?  And why can't I set the idle no less than 600 rpm? If I reconnect the vacuum line, the advance increases to 19 inch / hg (7 + 12), the idle is then too high and I couldn't decrease it with the idle screw!  I've re-read the Shop manual and there's something interesting: "during manufacturing the idle transfer port and the spark advance control port to the valves is carefully established for one particular assembly ...changing the port relationship would adversely effect normal carburetor operation between 15 & 30 mph..." This paragraph explains how to remove the throttle valves (staked screws) and I remember I've removed the valves to remove the throttle shaft. Maybe I've disturbed the correct position of the valves to ports when I reinstalled the valves? Could this explain why I couldn't adjust the idle (related to idle transfer port?)... I think I've got to disassembled the carburetor again or at last checked if the ports are under or below the valves...

Reply from Dick:

Yes, it sounds to me that there is a problem with the carburetor. If you have vacuum at the spark advance port (this is what I was calling ported vacuum, and Ken was calling "timed" port) as high as 12 mm hg at idle, there is definitely something amiss. Either the throttle plates are not positioned in the shaft correctly (my guess would be that they are upside down, such that the edge is not at the correct elevation with respect to the ports, this would also explain your idle speed setting difficulties), or else there is blockage or some other problem with the vacuum ports. I see from your quote of the FSM that there are two ports. Can you find the other one, and verify that you are connected to the correct one?

Question from John (1960):

I have been letting my car sit for the past 6 months & now it doesn't want to stay running when I let my foot off of the gas. The first time, the carb was spilling gas all over the engine & then it wouldn't restart. Now it seems as if it is starving for gas. I tried changing the fuel filter & thought that was it until it went from high idle & immediately stalled. It then refused to restart again & didn't flood, although I tried to start for several minutes, I sprayed a little carb cleaner into the carb & it again started but again stalled when I let off the gas. I'm thinking it may be the fuel pump, which was "borrowed" from another Imperial in 1990. Any advice?


From Matt:

Fuel pump is my guess.

From Paul:

It sounds like the fuel pump to me. All of my old cars had to have a new fuel pump recently. In addition to the pumps just being old and ready to fail, I have also heard that today's gas is particularly hard on the old diaphragm. The fact that you car ran with a shot of starting fluid, and then quit sounds like it isn't getting any gas.

From Chris:

Stuck floats. I've had terriffc success with this little fix on one of my lesser Chrysler products: Smack the top of the carburetor a few times with the plastic handle of a large screwdriver, right above where the fuel line enters the carb. This is on one of my Chargers that sits for several months without being started, once "wacked" it's fine until after it's set for another extended period of time...

From Russell:

Sounds like trash in the carb to me. Disconnect the fuel hose from the carb and run to a can, then crank the engine a little and see if you get gas in the can. If you do get gas there, it should be enough to get the car running. Reconnect the hose. It doesn't take much fuel pressure to fill the carb. If it still won't start, then it is probably in the carb. If there is no gas there then it probably is a bad fuel pump. It could be stuck floats. If so, you will have to pull the top of the carb off and clean it out and make sure the floats are free to move up and down. Make sure the needle and seat are not plugged with trash. Make sure the floats are at the correct adjustment.

From Larry:

Try first to check the fuel pressure. Then I would go to the carb possible could have dirt in the primary circuit causing it to stall at ilde.sometimes when the float in the carb can get saturated and will spill over into the engine.

Question from Zan (1962):

I had a problem tonight with my car stalling at low idle. I checked the fuel filter and it looks good. I've got a new fuel pump that's been working reliably for the last few months. For those who don't remember I got the funk out of my gas tank and it's been derustified. Lets see, the carb hasn't been giving me any headaches... so until proven otherwise I'll go with Dick B.'s wise words and worry about that last.

Reply from Dick:

First, when you increase the idle speed, either by feeding a little gas with your foot, or by adjusting the idle speed screw, does the car seem to idle smoothly, or is it missing and/or running rough?

If it runs smoothly, check for something having changed in the linkage or idle speed adjustment, or perhaps the timing has shifted (distributor loose?). Make sure the PCV valve is loose and will still rattle when you shake it (depending on where your car was delivered, it may not have a PCV valve). Make sure none of the vacuum lines connected to the intake manifold have fallen off (is everything working right that is vacuum operated - AC, Power brakes, brake release {if used on 62})?

If it seems to idle lumpy or seems rough running, check for the choke stuck on, or again, check the vacuum lines as above. If nothing seems out of order, you may have still yet another little particle of crud in your idle circuit. The quick cure to try is to gently seat the idle mixture screws one at a time, counting the turns so that later you can set them back exactly where they were. Once you feel the seat contact, back the screws all the way out (don't lose the little spring) and squirt some carburetor cleaner aerosol stuff right into each screw hole. If this is your problem, it will probably be fixed now, until the next time a piece of crud finds it's way through your gas filter. Replace the screws to the exact setting they had before, and try it.

If this turns out to be your problem, I think you should obtain another gas filter and put it in the line to the carburetor - get a metal cartridge type from NAPA or other parts store which sells good quality stuff. The glass ones are nice to look at, but in my experience seem to let some stuff through, especially if you are fighting really fine particles.

Your fuel pump would not be a cause for this problem -- fuel pump problems usually show up at high speed or under acceleration first.

Question from Denis (1962):

I've been having a rash of problems with two of my cars. I'll be pulling up to a stop light, take my foot off the gas to break, and the motor stalls, and will not restart, no matter what I do. Have it towed to the garage, they get in and it restarts, and won't stall out no matter what they do. Some days the cars have been running fine for hours, and some days I only get a block or two from the house and they stall out. Even changed the carb in this on and picked it up yesterday, and today it got towed to the garage, again. Tried changing the fuel pumps, tried rebuilding the carbs, tried cleaning the fuel lines, all cars have just had the gas tanks boiled out & realigning done on them. I've used up my AAA free towing in the first 2 months. I'm about to sell them for junk. Does anyone have any idea?


From Marc:

I had the same problem w/ my '67 - a phenolic spacer between the carb and intake manifold fixed it. The gas we have is so bad it boils out in the carb.

From John:

I had a '63 that did that when I first got it. I believe the problem was vapor lock. After a while, I could usually tell when it would probably stall & downshift into drive 2 or to neutral & give it some gas.. This car had sat the quite a number of years & after I started driving it regularly, the problem stopped without me doing anything. I had the car for about 16 years & the problem never returned. One suggestion is that it if you don't that piece of foil covered insulation below the carb, make one & place it there. Lowering the temp under the carb just a few degrees may make enough difference.

From Paul:

I have used up my AAA towing two years in a row on my 1980 Lincoln. One of the Imperials, lately the '55 and most recently the '62, have been my back up cars. My problems have been mainly ignition based, but I am beginning to sense some carburator trouble in the the air now too.

Don't give up! If both of your cars are doing the same thing, you are bound to get to the bottom of it sooner or later, and it will most likely be something really small.

Problems with ignition and carburation are very difficult to distinguish. Bottom line, it has to be one or the other or both. If you have the patience to wait it out, not only will you solve the problem but you will learn something interesting in the process.

Question from Jay (1962):

When I start my Imperial, I notice that she barely will keep an idle. When I step on the accelerator slightly, the engine smoothes right up and doesn't miss a beat. Take my foot off the gas and the idle goes back to being very rough (sounds like 200-300 rpm.)  We get to the stop sign safely and the engine almost dies. I popped the hood and at this point, the engine barely wants to idle and when shutting it down it makes a few terrible knocks. She brought us home some 4 hours later. She ran fine with the exception of her rough idle.  If heat is a definite factor, could vapor-lock be a possibility?  What exactly is vapor-lock? How does one prevent it?

Reply from Dick:

First, the pinging. If your timing is set to spec. (you have to check this after you set point dwell to spec.) most likely your engine has high enough compression, compounded by the fact that is undoubtedly has a buildup of carbon in the cylinders, and further compounded by the fact that it might have been running warmer than usual, then therefore and whereas all of the above, it is hereby resolved that you need to retard the timing to avoid damage to the engine from severe pinging. If it is only occurring once in a while, and only on part throttle at say 30 to 40 MPH, you are not in the danger zone, don't sweat it. Use 92 octane fuel and when it pings either
punch it toward the floor (the vacuum advance will retard the spark due to drop in intake vacuum) or back off the pedal, either should stop the racket.

Second, the rough idle. I take it that the engine pulls fine at higher RPM, and idles smooth if you feed it a little throttle. In this case, most
likely, your idle passages are crudded up with one or more pieces of the dreaded roving rust particles. Gently screw each idle mixture adjustment screw all the way in to the stop (I said gently!) and count the turns that each screw was out from the stop. Then take the screws all the way out (don't loose the little springs), keep track of which is which, and get a can of magic mechanic in a bottle type snake oil of the Carburetor Cleaner Spray persuasion. Place little plastic doo-hickey in each idle screw hole and give a mighty squirt. (Engine off). If you have access to a compressor (didn't we discuss this before?), set it at about 10 PSI and blow into the same two holes. Reinsert the screws to the stops, then back them out so you have the original settings. Problem gone? Yes?......Program terminates ( addition of another fuel filter at the carburetor inlet is recommended). No?......Go to plan B.

Plan B: Take off air cleaner, start engine, get it to idle somehow, not fast though, and clamber up on fender to get a good look with a flashlight down the great maw of the carburetor. See any liquid dribbling from anywhere? Yes......You are going to have to get a kit and go through the carburetor. This is a kitchen table operation, and requires careful study of the diagrams and instructions in the kit, and the rest of the carburetor spray. Do not allow the cat to scramble the parts. Do not turn the carburetor pieces over until you are sure all the little thingys are out of there and accounted for. This is not rocket science, you will not have any problem doing this.

Why the commercially rebuilt carburetors never seem to be done right I do not understand, but that is my experience. You are much better off to do it yourself.

If worse comes to worst, you can buy a new AFB for about $280 that will fit and work great, but you should not need to if all the problems are crud related.

As to the spark gap inaccuracy, I doubt if this is related to your pinging, and certainly not your idle problem. If the plugs are the correct ones for the car, you could try going to a one step cooler plug the next time, though, to help the pinging.

As for the knocking when you shut it off, this usually occurs when the engine is hot enough and is receiving enough fuel to run on as a diesel engine for a short time. This is hard on the bearings, as the phenomenon is the same as severe pinging. The usual cure is to reduce the amount of fuel available, for this reason later cars used an electrically operated solenoid to shut off the gas completely when the ignition is turned off.  Your car is trying to cope with the modern high vapor pressure fuels without this artifice. Probably your carburetor problem is causing more liquid fuel to enter the intake manifold at idle, and the cures suggested above should help. The lowest idle speed you can live with is the best one, for this same reason (running on problem).

Vapor Lock. This is defined as fuel being vaporized (usually due to high temperature) on the tank side of the fuel pump, so that the pump, which is designed to pump liquid, not vapor, will be unable to move fuel to the carburetor, and the car dies. This is most likely to happen after the car has been driven hard, shut down, allowed to heat soak for a while, then restarted and driven off. When the gas in the carburetor has been used up, (typically a block or so), the car will stumble and die. Upon inspection of the carburetor, it will be found to have no fuel. Often a car will begin to show this symptom after the fuel lines from the tank to the pump have aged, and develop a slight porosity. Since this line is under suction, any porosity causes an injection of air, rather than an loss of fuel. Thus it is often not detectable except by the fact that a car which never had vapor lock starts developing the symptom. The cure is to replace
all the rubber hoses which contact fuel with new ones, and be sure they show a SAE rating of "Fuel and Vapor, R9 spec" or equivalent.

Your symptoms are not those of Vapor Lock.

Question from Allison (1963):

I installed a new carburetor in the car and then let it sit for 4 days. This morning I started it...fired right up. One start is not a good test but so far it looks as though replacing the carburetor was the ticket. Now if I can just get my air cleaner situation settled!!! My old air cleaner won't fit my new carburetor.  It fits the carburetor perfectly, the diameter is right, coil and hoses are in the way. The new carburetor is lower profile than the old one. Either I need to find some sort of adapter to let the air cleaner sit higher or move everything out of the way.


From Roy:

The bottom piece of the air cleaner is shaped so it has a space for the coil, so you need to rotate it until that gap is above the coil. If it still doesn't fit then you can get one of the phenolic resin insulating spacers mentioned in the recent strings. (Looks like the gasket only much thicker and hard). I'm not sure which hoses you are talking about, but if it is the fuel line then the spacer under the carb won't help since the fuel line is relative to the carburetor. It sounds like your starting problem has been solved, likely because the carburetor is new but also because it has a new properly adjusted electric choke that closes properly. I mentioned the importance of proper choke adjustment several months ago, but nobody seemed to give it much credibility so I only mention it here in passing. Good luck, enjoy your quick getaways!

From Bill:

Most any auto parts store with speed accessories will have an adapter/spacer that you can use to raise the carb about 3/8ths to a 1/2 an inch. Should give you the clearance you need. Check the stud for the air cleaner to make sure it doesn't go too high and right through the hood when you close it. Been there, done that! Not pretty!

Question from Johan (1965):

I have no fuel squirting in to the bowl when I pump the carb (engine off). I have been having dead battery problems lately and have been pumping and starting allot (different problem now fixed). When I turn the engine over wouldn't pressure build up in the fuel system and remain after the ignition is turned off (provided the pump is working)? When I last drove it home about 1\2 mile and warmed up, it seemed to idle a hair fast and now I have this no fuel problem.

Oh yes, at one point I started to pull away from the curb and the engine completly died (electric was good), then got it home and started it up then died again and thats when I found no fuel going to the carb.

1965 LeBaron
Fuel line?
Can any one give me a clue?


From Dave:

Is it out of gas? I'm not kidding around, either, because I've done it. I went as far as replacing the fuel pump on my car before realizing I was out of gas once.

Another time, I replaced the pump when the problem was actually a pinched off fuel line.

From Rob:

We've been through similar questions before.

Had the car been sitting for a long time? Have you changed the fuel filter? In my case the tank was/is so rusty that the sediment would clog the filter and kill the car. A fairly easy test is to pull the hose on the tank side of the fuel pump and then submerge it in a container with clean fuel. If the car runs fine your problem is probably the tank. If not, it is most likely the pump. In my case, I took off the cap and blew through the hose into the tank with my compressor. It runs OK, but obviously the cure is a new tank. THE USUAL PRECAUTIONS ABOUT WORKING WITH FUEL, CONTAINERS AND FAN BELTS ETC. ALL APPLY.

From Julian:

There is a filter in the tank. You have to drop the tank partially to get the float out. The filter is at the end of the pick-up tube.

Question from Alan (1965):

I've just gotten my recently purchased '65 LeBaron back from the shop. Was having drive line and front end work. Took it out today and noticed that every time I accelerated there was a really loud gushing, gurgling sound. I mean this was so noticeable I thought Esther Williams was going to materialize through the fire wall and tell me the water's fine, jump in. Every time I'd pull away from a stop or pass another car it would happen again. There's nothing leaking or showing up anywhere so it's seemingly more annoying than a real problem but it is annoying and I wondered if anybody had any thoughts.


From Dick:

My guess would be that the air plenum in front of the windshield has filled with water (if you live in one of those unfortunate parts of the earth where water sometimes drops from the sky). There are drains to let this stuff escape, that come out through rubber flaps on the engine side of the firewall. Check them both for a build-up of leaves, rat droppings, cigarette butts or whatever else flies about in your local atmosphere. It is also possible that the AC plenum condensate drains are plugged up, but that seems less likely if the car has been sitting, not driven.

From Roger:

I've experienced that when there's a heater core problem. Could be either an air lock or a partially plugged core.

Question from JP (1965):

I have a sick '65 coupe and don't know how to diagnose. She's got a rough idle all the way to the point of dying when at a stop sign in drive unless I keep my foot on the throttle. After suspecting and rebuilding the carburetor I've determined 2 things. 1) I have a very nicely rebuilt carburetor, and 2) that wasn't the problem. The odd part is the car runs well when warming up and then for the first mile or two. Anyone got any ideas?


From Kne:

I would suspect it's running rich for some reason.

1. incorrect float setting?

2. Choke not opening all the way when warm. (easy to check)

From Lawrence:

At the risk of offending purists and the show-car crowd, at the first sign of choke problems, I remove all remnants of the automatic choke and install a hand-choke.  Kits are available at any parts store for less than $10 - properly installed (no kinks in cable, cable properly aligned with adequate supports, grease cable liberally with white lithium grease, locate choke handle in a convenient yet out of sight location)   Benefits: no more choke problems, you have an added degree of control over the start mixture and, to a limited degree, an active theft deterrent! Don't worry about forgetting to push the choke back in - your cars engine will remind you!

From Norm:

The choke pull-off is not working. That is a small diaphragm on the pass side of the carburetor which cracks open the choke so the car does not stall.

Follow-up from JP:

Are you talking about the vacuum actuated dashpot on that side of the carburetor, or the heat riser that mounts in the manifold?  I did not test these items, but I will now!!

Question from Brian (1966):

I was driving yesterday came up to a light and the car stalled. I restarted it but I had to put the pedal to the floor. I got it home but now it won't idle. I'm a little rusty, any ideas? I believe it has a Carter 4bbl/440 motor.

As soon as it happened I pulled the air cleaner and the choke was wide open but I noticed a steam (smoke like cloud coming out of the primaries). Could that be the floats being stuck? It runs great as long as it is above idle speed.


From Paul:

It sounds like it flooded. If there is black smoke when it is trying to idle, check to see if the choke is open. If the choke is wide open and you still have back smoke, the floats may be stuck. Could be other things too, but these are a good place to start.

If there is no black smoke, check for a massive vacuum leak.

From Dave:

Sounds like a "flooding" situation. AFBs are quite sensitive to any "dirt"/etc in the fuel. Replacing the carb needles/seats and the fuel filter and checking the gas tank for "trash" may be in order.

From Dick:

The "steam" you saw was probably condensed fuel vapor (extremely flammable!) - you might have smelled it?

If this is the case, and you feel up to it, take the top screws off the air horn (the cast top cover of the carburetor). You need to disconnected some attachments, and remove the two mixture control needles, but this is all pretty simple stuff, and you will not disturb any adjustments. Then look to see where the fuel level is. If one of the sections is almost overflowing with fuel, you know the float/needle valve system has failed. See if the float on that side (primary or secondary) has fuel inside it. (Take it off the air horn by sliding the pivot rod out of it's mounting, the shake it next to your ear). If it has fuel inside it, you've found your problem. These can be drained and soldered up, if you are handy with a soldering iron, or you can look for a new float assembly.

If the floats are empty, then the problem is most likely a piece of crud in the needle valve assembly itself. The best solution is to replace your fuel filter and do a complete cleaning of the carburetor (you'll need a kit from NAPA or other auto parts place). However, you can try just cleaning the fuel inlet screen, the needle valve and seat, and see if your problem goes away (and stays away?).

Good luck. This ain't rocket science, it's all just common sense. Be careful to note how things come apart, and keep track of all the pieces!

From Eric:

I have had a similar experience in my '72 Newport. One day, I slammed on the brakes. For a couple of days after, I heard a vacuum like whistle somewhere. Soon after, my car started running very poorly, accelerating like it had a severe vacuum leak. Feathering the accelerator was needed to get the motor to rev. Once at speed, the car ran smooth, tho I could tell a vacuum problem existed.

I found that when the brake vacuum hose to the brake booster was taken off and plugged, the car ran fine. I bought a new brake booster but have yet to put it on. After I bought the new booster, it came to mind that it may just be the seal around the one way valve button on the booster that failed, this part fits loose enough to lose vacuum. I'm in the process of deducing the problem.

From David:

I have a '66 and had the same problem, upon looking for the fuel filter I noticed there wasn't one, someone before me removed it. You may need to put one in. Clean the carb, check the float setting (mine were incorrect) the correct float setting will be in the imperial service manual. Put some dry gas in with high tech and that should take care of the problem. Might also pull the plugs and have a look at em, they tell the story of how your car runs.

Question from Norm (1966):

I am looking for help with an annoying problem. The carburetor on my '66 convertible works perfectly except in one condition: WOT during DOWNSHIFT. It Stumbles and surges in that condition. Oddly, it will not stumble or surge if WOT is accomplished without downshift.  It will take all the throttle I can give it and I can hear the secondaries opening up, but the second the trans downshifts, it starts to surge and stumble. Only when the rev's come up does the engine stumble. I am certain this is a carb problem as this carb produces the same result on another car that previously did not have the problem. Note the floats are set correctly, the unit is clean and still has its original 2-stage metering rods and it was not one of those equipped with an auxiliary secondary air valve.


From Kne:

Here's my nickel ninety-eight: 

1) You are probably "o.k." not to replace the ball, although you should if possible. But if it wasn't corroded it may have been better not to damage anything, especially if a new metal retaining piece was not included in the kit. 

2) This is tough, as you never know if the last guy used the right gasket. Generally you want to match the old and new, but I have taken carburetors apart that I suspected had the wrong gasket. I guess you just have to study it and really think about what each passage does, and sometimes some are blocked off by the gasket on purpose. I think I would match gaskets first and then if it didn't work right I'd experiment with different ones. 

3) On the AFB, I don't think there is really anyplace for the gas to leak to unless there is a crack. On a hot running engine sometimes the gas will boil out through the boosters after shutdown. Perhaps enough boils out that the remainder evaporates after two days? Wild guess. Couldn't hurt to put the carburetor up on a short (1/2" or 1/4") insulated spacer and see what happens. (?) 

4) Well I would replace an accelerator pump any chance I got. How much pump shot you get is adjustable, usually three different holes to put the linkage in and you can bend the linkage to the pump to get optimum pump shot, are you familiar with this? Not too hard to figure out if you stare at it enough and play around with it. Is it possible that the accelerator pump linkage was bent, or installed in a different hole when you re-assembled? Also make sure that the check ball or needle check valve is in that passage from the pump chamber to the squirters. Tends to fall out without noticing before you get the top back on sometimes.

Also, if gas is boiling in your fuel pump or the line from the pump to the carburetor, the vapor will reach a high enough pressure to force the carburetor's needle valve off the seat, and push the gas out of the carburetor and into the manifold.  I always route that line from the pump away from the engine instead of up the front as in the stock location.

Follow-up from Jim:

I once had a car with the fuel line routed way away from the engine but then it was in the air flow coming from the radiator. I move it back to the stock location (near the block) and converted back to steel instead of the copper that somebody cobbled, and my vapor lock problems vanished.

Question from Greg (1967):

My '67 has a new gas tank, new metal lines, new fuel pump, new filter, and new rubber lines. All connections are solid. The car is a bit hard starting, but nothing really worth talking about in this posting. The idle is very slightly rough, but still smooth when compared to most cars. The car will idle just fine in park for about 2 minutes, then stalls out and dies, almost like fuel starvation. It will not restart unless you wait about 5 minutes. I can also start the car and rev the engine, using much more gas and making all sorts of enjoyable noises while doing so, but the car again stalls and dies in about 2 minutes. Because the car stalls and dies after about the same length of time, regardless of engine speed before that, I'm beginning to think that the stalling is related to something that results or changes due to reaching normal operating conditions, like
manifold pressure, pressure in the tank (new vented cap with correct PSI rating), choke, vacuum (although the brake booster has full power), etc. Any ideas?


From Dick:

This is certainly a strange malady! Let me guess: Do you have a Holley carburetor? Thought so.

To start gathering data, next time it dies like this, before you do anything else, take off the air cleaner and watch the accelerator pump nozzle while you operate the accelerator linkage. See if there is a stream of gas from the nozzles. If not, your float needle valve is sticking shut for some reason, and when you crank the engine slowly, the fuel pump isn't popping it open. So it is possible that your needle valve is worn.

If there is a healthy squirt from the accelerator pump nozzles, then I suspect your car is flooding out when it dies. You don't mention clouds of black smoke when you restart, but this would be another indication of flooding. If this is the case, you still have a float problem, probably the float level is set too high. Even more likely, if and only if it is a Holley, is an internal leak in the carburetor - probably at the power valve.

From Robert:

Check to be sure your exhaust system is not plugged up somewhere. I encountered this once on a 1966 where the exhaust pipe just past the manifold had internally collapsed although it looked OK outside. Once this was replaced, the car ran fine again.

Follow-up from Greg:

Last week I posted that the '67 would run fine for 2 minutes and then stall out, as if it were experiencing fuel starvation. The car has a new tank, new metal lines, a new pump, a new filter, and new lines from the pump to the carb. I pulled the Holley carb and found that the previous owner had rebuilt the carb quite recently, most of the gaskets, etc looked brand new. I haven't put many miles on the car at all. I did find that the primary float was out of adjustment and, when in the "full up" position, was completely cutting off the fuel to that float bowl. It could have been that the float was sticking in that position even when the fuel level went down. I adjusted the float and made sure that it still allowed just a bit of fuel, even in the "full up" position. I still have exactly the same problem. The car runs fine for 2 minutes or so, then I can hear the engine rpm drop ever so slightly, as if it had reached normal operating conditions, then the car will stall out and die within 5 seconds. When I pulled the carb again, I found that the same primary chamber still had very little fuel in it, although it is now impossible for the flow of fuel to that chamber to be cut off completely. I've checked the lines, and a mouthful of fuel suggests that there are no obstructions. The secondary float bowl is full of gas. Could it be that I have missed something? The interior of the carb is scrubbed clean. Could it be electrical.... like the coil gets warmed up after 2 minutes and then fails?

Reply from Dick:

Don't go wandering off into the ignition or other areas.

The absence of fuel in the front half of the carburetor indicates that your problem is right there. The fuel level in the carburetor should always be exactly what the specification calls for. The correct setting for the float valve WILL completely block off fuel inlet at that level, but will again allow fuel to enter when the level drops away from that point. I suspect your float valve is sticking in the shut position, due to a bad valve or incorrect assembly.

To track this down, run the car until it dies again, and then blow INTO The carburetor fuel inlet before you disturb the carburetor or the inlet line in any way (you'll have to set up to do this in advance so you don't jiggle and unstick the offending valve - perhaps you can temporarily splice in a rubber hose length so that you can disconnect it and blow toward the carburetor without disturbing anything). If you can't blow air into the carb inlet, you know the valve is stuck! It should be wide open when the fuel level is below the correct level.

Reply from Jim:

Did you also change the filter "sock" that is part of the pick up tube in the tank? It may be cogged to the point that it won't let sufficient gas through to keep up with what the engine uses but will let enough "soak through" when the engine shuts off to allow it to start and run a few minutes. I suppose the same theory could apply to an in line paper filter too. I once heard of a rubber line which had collapsed internally cutting off fuel flow intermittently.

I agree with a lot of the other answers in that its most likely not ignition-related. The engine is using the gas faster than it can get more whatever the cause.

I also agree that he float should not let fuel through in the "full up" position. Once your real problem is fixed, this will lead to flooding and/or fire. The float is there to keep the fuel at the proper level in the carb. and it can't do that unless it can shut it off momentarily when its reached that level.

Question from (1967):

Spring is here and I can continue working on the Imperial. A brief history; My '67 originally came with a Holley carb and after two rebuilds, mixture needles that wouldn't play nice, and a very rich running engine, I decided to install a new Carter AFB with 750cfm. No, this is not a discussion about the 750cfm. The carb arrived and was beautiful; it was rebuilt like new, tested on another vehicle and ran perfectly, and bolted right onto the 440 with no problems. The Carter did not have a choke, but I plan to install one shortly. All internal parts in the Carter were new, and the only thing lacking was the carb to manifold gasket. I used the gasket from one of my Holley rebuild kits as it was new and appeared to mate flawlessly to the new carb. Now the car will not start. I have checked fuel delivery and it's just about perfect. New plugs, wires, disty cap, rotor, starter solenoid, and coil. Crankity, crankity, cark. No start. I did manage to get the engine to catch once on a 65 degree day, with the choke wired 90% shut, but no amount of feathering the gas, operating the choke butterfly manually, or begging a higher power would make it continue to run. Could it be this gasket? Is it covering some opening on the underside of the carb that should be open? Doubt that it's a vaporization problem since the engine never runs and therefore never builds up any heat. As usual, I await anxiously for the greater wisdom of the mailing list to help me to get this car on the road as soon as possible. Also, any leads for a choke?

Reply from Demetrios:

The not perfectly fitting gasket would not prevent the car from starting, but you do need to clean it up and remove all gasket material from obstracting the air flow.

I would suggest you buy a can of starting fluid (ether) and see if the car will start with it. If the car runs on starting fluid, then certainly the carb is not functioning. If the car does not start with starting fluid, your problem is ignition.

By the way, a properly functioning carb should be smelling gasoline when you pump the gas pedal many times.

Question from Bob (1968):

I have a '68 Crown with the 440 and Holley carb. The carb was supposedly professionally rebuilt by the previous owner before I purchased the car 6 months ago, and he provided receipts to verify this. The fuel pump was also replaced. The car has been hard to start from the day I received it, and now has developed a "gallop" or surging at slow idle. When the car sits idling after the engine is hot, it sounds like it has a racing cam in it. Any suggestions on where to start to correct the problem?


From Dick:

As I'm sure you realize, there are so many possible causes that it would only be a wild chance that one could diagnose it for you without seeing the car. If you have access to someone with an engine analyzer, they could track it down for you immediately. Failing that, you will have to try different things until you hit on the right cause.

Since you have a Holley carburetor, that is indeed always a suspect in poor idle situations. If you have access to another carburetor, you could try just swapping it temporarily (it only takes about 15 minutes to swap a carburetor), that would nail down whether or not the dreaded Holley is the culprit. If you smell gas around the engine, it is almost surely at least part of the problem. The usual failure for these is internal leakage, which you cannot see but you can hear, if you remove the air cleaner and listen for a dribbling sound from the air horn area.

Rebuilt carburetors are often the source of trouble - the best success has come from replacing these with new AFBs, which are readily available for less than $300.

However, your problem might have nothing at all to do with the carburetor - you really should have it diagnosed by a professional before you start throwing money at it.

From Brian:

I personally like the holleys. Don't get me wrong, the Carters are great carbs. If Holleys are such a bad carburetor, why is it that Holleys are the preferred carb for high performance or racing? I have holleys on both my Imp and my 300 and have had no problem. The one on the Imp needs rebuilt, but has not been touched for 6 years. The 300 has a crusty fuel tank and plugs up a filter in about a week(tank full). It has been on there for two years and still runs great. Like I said, I like holleys and see nothing wrong with them.

Reply from Elijah:

Probably because Holley carbs offer more options for performance tweaking. And since racers generally tune the car before each run, this is an advantage.

An Imperial, however, is a dignified, luxury automobile. The owner of an Imperial should not be expected to pop the hood and fiddle with the carburetor each time he or she plans to drive the car.

The Carter offers comparable performance, but with MUCH greater dependability. An AFB is probably the closest thing to a "bullet-proof" carburetor ever made, and the AVS is a close second. AND even the novice can generally get good results from rebuilding an AFB or AVS (which can't be said of either the Holley or the Carter ThermoQuad).

Question from Bob (1969):

I had some problems with my carburetor and replaced the Holley with a substitute, but the shop where I had it rebuilt gave me a rebuilt carburetor from Holley for another thirty bucks. After putting it on and a little tuning, the car starts right up and seems to idle very well. But after driving only about a quarter mile the throttle seems to have a mind of its own. The old carburetor was doing the same thing. The gas peddle will not return unless I turn the car off. But if I rev the engine in park, there is no problem. Am I missing some kind of link between the carburetor and tranny (vacuum line?). The linkage for the new carburetor hooked up just fine and does not stick while in park. Anyone else ever have a problem like this?

Reply from John:

My 69 did the same thing when it got fairly cold out & I wasn't using the car much. Now that I'm out here in AZ, cold is not a problem any more. I believe the problem is in the cable. There are a couple of spots that are supposed to be lubed once & awhile. 

Question from Roger (1969):

I took my '69 Imperial in to solve an exhaust leak.  I had to pull the head but it already had a bolt broken off.  I also took a cut on the manifold to make sure it was flat.  I also put in new plugs, new plug wires, electronic module.  Now the car has kind of a looping idle but when I accelerate it runs right out very smooth. Any of you folks have any  idea about what's wrong?  


From Jack:

The looping sounds like carburetor problems. Weak metering rod springs, or a power valve needs replaced. What kind of carburetor is on your 69? A Carter AVS, AFB, Holley?

Follow-up from Roger:

The carburetor is a Holly.   I found two vacuum lines disconnected behind the carburetor.  They run up to the front of the engine compartment to two round black plastic devices. The engine seems to idle better now, but I don't think those two lines have anything to do with the carburetor.

Reply from Jack:

Vacuum leaks (small) will usually make the engine idle faster, on the other hand, a large leak will kill the engine. Holly carburetors have a power valve that can cause problems, also the float adjustment is critical. Many Holly carburetors also get internal leaks. If fuel is leaking from the float bowl into the venturi, it may cause the looping you describe. I would rebuild the carburetor (if there is not much play in the throttle shaft) or replace with a rebuilt or new one.

Question from Roger (1969):

I drove my '69 Imperial from Charlotte, NC up to Richmond, VA yesterday.  I stopped twice and the car would start right up with no problems but when I went to leave after it has been sitting awhile,  the car started hard and the idle was terrible.   I had to turn the idle screw way up to keep from stalling at stop lights and it would only restart if I held the accelerator to the floor.  I checked the vacuum lines, spark plug wires and they are all on. Any ideas?


From Dick:

If you have a Holley 4160 Carburetor, you most likely have the common, dreaded leakage problem from the fuel reservoirs in the end caps of the carburetor. Try tightening (very slightly! Don't over do this.) the 4 large screws on each end of the carburetor which hold the front and rear end caps on. If this helps or eliminates the problem temporarily, start looking for an AFB or AVS carburetor to put on the next time it starts to leak.

Once these carburetors have been over-tightened, the metal parts warp and there is no way to make the carburetor stop leaking permanently. The leak can be internal, making the car run as you describe, or it can be external, which you would have seen when you tweaked the idle.

If it was a fuel filter problem, the problem would not likely have affected the idle. Most likely that would show up when your driving situation required a large supply of guzzeline.

Follow-up from Roger:

I just gave the carburetor a couple of light raps with rubber mallet and lightly tighten the end cap screws. When I opened the hood I could smell gas and it looks like some has leaked from the carburetor.  The cars still idles rough but seems better. The carburetor is a Holley 4160 . Could you tell me about the AFB & AVS carburetors are and will they be correct for a car show?

Reply from Dick:

The AVS and AFB carburetors are Carters, and they were used interchangeably on Imperials. The lucky folk got the Carters, the unlucky got the Carters (my opinion; this will set off a howl, so brace yourself!). The AFB is readily available as it is still in production, the AVS is not available new, that I have heard, but they are such good carburetors that a professional rebuilt from an experienced shop (I don't mean one of the chain stores, I mean a real carburetor shop with a flow tester) should be trustworthy, or even one off a parts car.

The AFB was used only until mid 67, so strictly speaking it would not be exactly right for your car, but I doubt very much any one would notice the difference. You'll need someone to help you figure out linkage differences if any, and re-routing the fuel line. Some have had trouble fitting the air cleaner, but I think you'll be all right there as I believe the air cleaner was the same in 69 regardless of carburetor.

Question from Roger (1969):

I am still having some problem with my carburetor.  It is set way too rich.  When I first start it, I get black smoke but when the car warms up, it is ok.  1969 Imp with Holley carburetor... how do you adjust the automatic choke?

Reply from Dick:

I'd say the first thing to check is the vacuum pull-off diaphragm. This is the device on the side of the carburetor that is set up to pull the choke butterfly open when vacuum is present at the diaphragm input. You should be able to suck on this hose and see the choke open up, and you should not be able to notice any leakage (air flowing in the tubing) at all. If you pull a little vacuum on it, and just seal it off with the tip of your tongue, it should stay pulled in all the way (choke open all the way). This is the device that modulates the amount of choking while the car is warming up. Often the little rubber hose that operates it is either connected to the wrong port, or is leaking. The hose is supposed to be connected to the vacuum port that is sticking out of the base of the carburetor, just toward the center from the front left (passenger side) carburetor mounting bolt.

Holley 4160's are famous for another problem which causes black smoke, but it doesn't go away with warming up. This is the dreaded leakage problem. You don' t seem to have it, so don't tighten down on the 8 screws that hold the float chambers to the body. That is what lands most of these in the junk bin (overtightening to cure the damn leaks).

Question from Paul (1972):

My '72 440 runs strong but has a poor quality idle. It stales sometimes.  The car had been sitting (never run) for about 12-15 years. What can I do to smooth out the otherwise great running motor? 


From Dick:

Well, Paul, we have to take this in steps.

Step one is, have a compression test done on the engine. If all 8 are within + or - 10% of each other, the car can be made to idle well. If they are further out of agreement than that, you most likely have a burned exhaust valve, which you can also hear at the tailpipe if the exhaust system is in good shape. A burned exhaust valve will make a chuff-chuff sound every time the affected cylinder fires. Other causes of low compression on a cylinder are of course also possible, these can be sorted out by holding each cylinder in turn at TDC and pumping air into the spark plug hole, while listening at the crankcase vent, carburetor, and exhaust pipe for where the air is leaking out.

If you have even compression, it's time to investigate the Carburetor. If you feel up to it, get a kit and rebuild it yourself (store bought rebuilds are almost always poorly done, in my experience), or failing that, find an old time carburetor shop and take the car there. If you want to try something first on the carburetor, take out the idle mixture screws, first noting how many turns each one was set from all the way seated. Then take the straw from your handy-dandy can of spray carburetor cleaner, and stick it in each screw hole, and give a short squirt in there. Then reinsert the idle screws to the same setting. I hope the setting is the same on both screws, and somewhere around two turns out from seated. If not, try that as an initial setting, then fine tune them watching the vacuum gauge,
trying for best idle (highest RPM with smooth idle.)

If the power is normal at higher RPM, we are assured that you have no serious timing error, or valve timing problems, so I am basing the above on that information. If you think the power might be down from normal ( a 440 should go like stink when you step on the loud pedal!), then you might have other problems, and the car should be seen by someone with an engine analyzer. Where are you located?

From Leo:

Rebuild the carburetor-change the fuel filter, take on highway to burn the junk out. Classic case of hypofreewayosis

Question from David (1973):

It's hard to start my '73 Imperial when cold (meaning beginning of day, not winter) with a couple of minutes turning over but it eventually fires. Of course it will fire right up by squirting some gas in the carburetor, but I'm not looking to that as a permanent fix. Anyone have any ideas on what this may be?


From Richard:

My '73 had the same problem with starting. I had the carburetor rebuilt by Larry Isgron at of Long Island N.Y. His phone number is 516-897-0401. He charged me $190 for the rebuilt including shipping. His turn around time is about 1 week. I've had several carbs done by him, and all came back looking like brand new. Just bolt the carburetor on the car, and you're ready to drive. He has them all adjusted in his shop on a motor before they leave. I highly recommend this man his work is that good.

From Paul:

There could be a vacuum leak somewhere in your car. It could also be the little primer jets are plugged up. I had this problem on my '63 and was able to clear them with a piece of wire from a shipping tag. It was just small enough, and flexible enough to work into the hole and free the little ball into doing its job.

The cars symptoms were exactly what you said. It always started fine except for the first time each day.

From Demetrios:

Does your choke plate close when you pump the throttle a couple of times when cold? To check this, just remove the air cleaner and look into the carburetor. The choke plate (a thin metal plate above the primary throttles) should close automatically when you do this. If its not, that is your problem. You can close it manually to confirm (force it closed while you manually pump the throttle linkage with your other hand). Once the choke closes, the engine should fire up quickly.

However, a cold 440 should start even without a choke. A cold engine needs rich mixture to start, which is exactly what the choke does. You can pump the throttle instead, and the accelerator pump will squirt extra gas to do the trick. It is not as effective, but it is easier on your gas bill, and it forces less gas dilution in the oil (I have disconnected the choke on both my 440's). However, in order for this to work, the accelerator pump needs to work. You can check this by looking into the carburetor while you pump the throttle linkage by hand. You should see small amounts of gas pumped right in. You should even be able to smell it (assuming the car has not ran for a while, if it has, you may be smelling the gas from the previous run).

You may have both issues going on. Replacing the accelerator pump may not require complete carburetor rebuilt. The non functioning auto choke may be the diathermal spring on the manifold.

From Kerry:

What is happening is the gas is draining out of the carburetor bowl and the cranking has to continue until gas is pumped up to the carburetor. Unfortunately the leakage is most likely due to a crack in the phenolic Thermoquad body. If I had kept my 73's I'd have replaced the TQ (mine was new (rebuilt) and still sucked) with a new carter and elect choke. Elijah has this carburetor on his '71 and it starts immediately even after sitting for days. Other people tell similar stories of the Carter.

Question from Bruce (1978):

I have carb problem with the mighty '78 NYB. Smog approval required that I spend a small fortune on a new carb. I had the work done at a local place that does only old cars, is run by a guy older than 55 and has done good work for me in the past. Bottom line, the car finally passed the smog, but now runs very poorly. The mechanic tells me that the severe exhaust leaks that the car has (manifold gasket, flange/connector after the manifold, resonator, etc.) cause the carb to perform badly. Does anyone know if this is reasonable? He also says that "none of these carbs for this car were ever any good." This sounds like nonsense to me, but the smog place claims to have screwed with the thing for 4 hours to get it to pass. The symptoms are rough ilde after car is warm and stalling when I punch the gas when the car is under no load(coasting or in neutral). Idle is also set way high, probably to mask the rough idle. Any comments? Has anyone had GOOD luck with replacement or rebuilt
carbs for this car? If I take off all the smog stuff and plug up the vacuum hoses, should that help?


From Miles:

There's a good chance you got a "bad" rebuilt carburetor. I know it sounds weird, but many rebuilt carbs don't work very well. You might consider getting it tested. There is a spot where the throttle shaft, or shafts go through the bottom of the carb. Many times rebuild places won't fix this, so a little vacuum is leaking in all the time, which is bad. The 55 year old guy might be right about those carbs not being so great, even when new.

But, before that...

First, I would have all those exhaust leaks fixed. They will never get the car to run right if they don't get that ironed out. Have them look for any vacuum leaks. Fix anything else on the car that might be giving you those problems. Have them replace all those little vacuum hoses that help the emissions system work. (or just chec to see if they are cracked, and leaking vacuum) Have them check to see if those hoses are properly routed. Check the Air Pump, Like the E.G.R. valve. That's a good one. When those go bad, there is a big vacuum leak! It's O.K. to bring a car right back to the shop if it runs really poorly. They probably did spens alot of time making your car ru as "lean" as possible, in order to have it pass smog.

And then have the shop adjust everything so the car runs the best. You don't have to keep the car set the way it is right now, just have it set that way during smog-check time.

Usually, if it's not just a worn out engine, the car will run poorly for a bunch of little reasons, not one big one. So, finding the fix is not so straight forward.

From Robin:

Quite honestly I think that is a load of crap. This car probably has a Thermoquad which has always worked very well for me. Matter of fact I have no problems with any Carter carbs AFB,AVS or Thermoquad.I think you are being taken for a ride.

From Rolland:

I am not sure what the original equipment carburetor was on the '78 New Yorker but I believe it was a Carter Thermo Quad. If you replaced it with a Thermo Quad and the rest of the engine (valves, plugs, plug wires, etc) are in good condition you should be able to get the car to idle and run well when it is warmed up. The weakness on these cars was warm up driveability. They did not do well just after starting (the second time) and during warm up. You just have to live with this.

There are a few critical areas you should check if you have a Thermo Quad carburetor. These did need periodic maintenance. Maybe once every two years they had to be gone over.

I would not remove any of the anti-pollution devices assuming they are correct and operating properly. Also I doubt that the exhaust leaks are causing much if any of the problem.

First I would check to be sure the timing is near 8 degrees BTDC. Then I would check the carburetor float level. With the air horn inverted the distance from the gasket to the bottom of the float should be 29/32. I would then readjust the engine idle speed to 750 rpm. This is the correct specification but may seem a little fast since most engines idle between 550 and 650 rpm. Then I would adjust the idle mixture screws one at a time (I expect you will have to force the plastic caps off to get at the screw) until you get the smoothest idle. You may have to readjust the idle speed.

Finally I would adjust the secondary air valve spring. This may be causing the stumble when you floor it with no load. You should get a carburetor book to find the air valve adjustment plug so you can remove it and get at the spring adjustment. Turn the spring adjusting screw with a screw driver until the valve just closes then turn it 1 1/4 turns more.

These are the critical adjustments on this carburetor. If it is a TQ you should be able to get it to run smooth and perform well when the engine is warm.

From Kerry:

Sounds like a vacuum leak to me. Thermoquads have issues but are good carbs overall.

From Brad:

First you have to be certain you have no vacuum leaks. No good doing anything until those are found. There's little chance anything to do with the exhaust system is going to make the engine run poorly. I run three Thermoquads and they are all great.

Next, from your description of what they did to your car, I would have to guess that they screwed in the idle mixture adjusting screws and then to compensate for the lean idle, they cranked up the idle adjustment. This would create the leanest mixture at idle possible. I also know from experience that those idle mixture screwes have a profound effect on that bogging down effect when you press on the throttle. I'd start by seeing how far out those screws are turned. You can see them on the front base of the carb, they have springs on them. Turn each one in while counting the turns so you can turn them back to the same place if needed. Typically these screws should be between 3 and 4.5 turns out.

Thirdly, get a new mechanic, this guy is obviously drunk.

From Mark:

I think Kerry is right. I had an '80 Buick with the exact same problem. It turned out the intake was leaking and after I sealed it up, my gas mileage went to 32MPG on the hwy. I had several '77-'78 C bodies and they all acted like yours and after rebuiding the Thermoquad, they ran the same. So look elsewhere, your carb guy is wrong. I had both manifold gaskets replaced and it didn't affect the Thermoquad one bit.

Question from Leo (1983):

Two days ago, I was at my daughters for supper and upon leaving, my 83 refused to start, not even a peep! After getting out to kick the tires I found it was flooded to the point I could smell raw gas very strongly. The next AM I went and disconnected the battery to reset the computer (such as it is) and made sure the air cleaner lid was tight and lo and behold, it started immediately. However, later on it started to die at stop lights and signs. Finally it again refused to start until I put the throttle on the floor and then relalized it was flooded again. It would start and then run rough until the extra gas is gone, then flood itself (I think) while moving. I finally ran the battery down enough to call AAA and tow her home. Tried it today and it starts fine then runs very rough, misses as tho several plugs were fouled?


From Dick:

My first, second and third guesses are all the same: You have a leak in the fuel line plumbing from the Control Fuel Pump to the Fuel Pressure Switch, or from there to the nozzle regulator/fuel rail assembly. Do the "run the car without the air cleaner lid on" trick and just look for where the liquid fuel is leaking from - I'm sure you'll see it. Possibly the FPS has developed a leak - it happens.

Since you didn't see a fluid leak, the control pump must be putting out too much fuel. Next, you'll have to beg, borrow or steal a voltmeter, and put it on the 23 volt power supply output - any place you can get on the violet #18 wire, probably on the throttle position sensor is the easy place. If the 23 volts is within a half volt or so of nominal, I suspect the either driver for the control fuel pump or the FPS has failed. You'll note that one of the wires to the control fuel pump is ground, the other is a variable voltage ranging from 0- to 12 volts, depending on fuel demand. If yours is stuck up near 12 volts, either the driver has failed or your high resistance FPS is fouling you up. Try unplugging the wire off the FPS and temporarily putting a clip lead from the wire to ground AFTER the engine starts. If this stops the flooding, you need a replacement FPS.

Otherwise, you have a bad power module. If you have a spare power module, try switching it. If you don't, pull yours and send it to me, I'll take a crack at repairing it for you (but don't be in a hurry!).

You can also contact one of the vendors on the IML list to see if you can buy a spare power module. One place I'm pretty sure you can get one is from Bob Baker at

Your FPS reading is somewhat high (but not outrageous), but since these are so hard to find, I can only suggest that you test it as described above to see if the flooding stops. If it does, then we are on a quest for a replacement FPS.

From Mike:

While I am by no means an EFI expert, I've been around these parts enough to know that the air box seal is a common malady of these systems. Seeing as how you paid particular attention to the air box seal, and the car started, I'd say there might be something causing the seal to loosen as the engine is running- either the seals could be bad, or the hardware holding the box closed could be faulty.

From Bob:

This sounds very much like a power module gone bad. There is a component that goes bad in it that causes the car to run way too rich. There is a small possibility that your coolant temperature switch has gone bad, but it usually doesn't cause this major of a problem.

From Bob:

I will try to help, it is very hard to analyize EFI problems at long distance, but I'll try. First off - I suggest that you have some collection of parts, known to be good, as substitutes; i.e. Power Module, CCC, Hydraulic Support Plate; I would think these to be less important: Water Temp Sensor, Auto Shutdown Module, and the two electrical resistors. Your flooding can be caused for a variety of reasons. You must also have a Digital VOM. The major parts of this EFI can be tested by the Imperial EFI Tester, without this you'll need the inventory of spare parts.

My problems like this were caused by a defective Pick-Up Coil in the distributer. The only sure way I solved that problem was to remove it, attach the ohmeter to the leads, warm it up with a hair dryer and watch the meter - sure enough, with a little heat the coil would open and the meter would show loss of continuity. Wait a little while and it could be repeated. New one necessary. If you haven't altered the idle speed recently then you should not be overly concerned about the adjustment, but if it was adjusted, look at the Idle Speed Motor arm and make sure that it is in the correct position with the engine not running.

To test the Power Module. connect the VOM to Terminals 7 and ground; attach two other leads from the battery, the positive to module terminal 3, the other to ground. When you finally connect the positive terminal, you should see 23 volts DC on the meter. If not, this part is defective - rebuild required.

A far fetched reason for this condition would be dirt particles clogging the two injector valves in their respective pockets - this would keep them open allowing fuel to flow continuously until it flooded out and stalled.

Another reason is that the Fuel Pressure Switch is remaining open, (electrically closed), allowing an excess rate of fuel flow to flood the engine and stall it. This switch may not repeat this fault every single time, hence a short run may feel okay, then another start and flood-out could result. You might want to replace this switch with one known to be good or test it. The insides of this switch are like the bottom of an oil can, upon certain pressure the disc will click open, reducing the speed of the pump and drop the fuel flow. You can test this by applying a low pressure from an air gun and feel the switch "oil can" in your hand - also hear it. Replace if defective.

Try these things and get back if you need more help. Try to ascertain that the Pump is indeed running at the higher speed causing this flooding.


Tip from Rolland about the poor, cold operation of a Thermoquad:

I owned a '74 New Yorker with a 440 and a Thermoquad. My experience was similar to what I am hearing. The warm up drivability was never good. I drove it about 100,000 miles and during that time I rebuilt the carburetor 3 or 4 times. The rebuild consisted of new gaskets, needle and seat and very meticulous attention to all specifications and adjustments. After the rebuild it would be acceptable for 10,000 miles or so then begin to deteriorate. I like the carburetor when it was working well but it just did not seem to have the durability. Fuel economy was good by '74 standards (17 to 18 on the highway). One trick I tried for a period of time that seemed to improve the warm up drivability was to disconnect the choke heater wire to keep the choke on longer. During cold weather (here in Illinois) that helped quite a bit.

From Kne:

If you don't want to pump the pedal 30 times to start, put in an electric fuel pump. It will start just like a fuel injected engine.

From Dietmar:

What you describe is exactly what happens to everybody with original Thermoquads or Quadrajets.  The warm up period is a very sensible and complicated balance between all mechanical parts of the carburetor and your foot. So if you start and drive around, you will have continuously different conditions in your carburetor until the choke has opened the starter throttle completely. During this period you have to use your pedal very sensible and with much feeling to the respond because the carburetor is always in a critical situation to stall, especially when you open the throttle suddenly to pass or at a traffic light. The warm up driving needs a well adjusted carburetor and perfect mechanical linkages. This is the problem today. The carburetors and engines are not maintained as well and the original carburetor linkages tend to get rotten or at least far away from being precise. That's why I always recommend Edelbrocks with electric choke. So start and drive carefully the first five minutes!

From Joe:

Having had a 73 New Yorker with a Thermoquad, the usual problem with having to crank and pump and pump after sitting a while is due to the phenolic center body where the fuel bowl is located developing thin hairline cracks which allow the gasoline to leak out. Thus the bowl has to be refilled before the accelerator plunger can spray any fuel down the throat. The easiest fix is to just buy a rebuilt Thermoquad carburetor through a good car parts dealer.

From E:

All older cars must be warmed up. It is something you simply have to get used to. I warm up my engine. And also allow my engine to cool down some before I shut it off. Newer cars have spoiled some of us impatient people. I have started my 62 Imperial several time after long periods of rest and it always starts for me first try. I have worked on all sizes of vehicles, and at work I drive heavy machinery and large trucks on a daily basis. They also require a warm up. I have a few tips for you guys having all this trouble starting.  Turn on the key and give it a few good pumps on the gas. 4 is about what I use on my Imperial and the gas trucks at work. If you pump it too much, 6+ it will be flooded and hard to start.   As you begin cranking the engine feather (pumping action- but don't put it all the way to the floor, pump about the first half of the pedals range or so)  It will cough a couple times and then start revving slightly.  Now hold it at a high idle well above its regular idle speed for a few seconds (maybe 10 or so).  Now let off the gas completely and see if it will idle by itself. If it begins to sputter like it is going to die, begin feathering the gas again.

And lastly never shut of the engine from anything above an idle let it sit for just a like 5 seconds at an idle before you turn the key off. All these numbers are estimates, kind of an average from my experiences.  Play with it a little bit.  It will save you on batteries and starters in the long run.

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