4-barrel Rochester stalls on acceleration

[gmdbhornet]

Need a little advice.

I have a 1963 Buick Wildcat 401 nailhead ( 33, 000 original miles) with a Rochester Carburetor. I just rebuilt the carburetor placed it on the car adjusted the dwell, set the ignition timing, adjusted the carburetor, and installed a new fuel filter. The enigine is smooth at idle, but when I accelerate from a stopped position at low speeds the engine just stops as if its not running and then either stalls or starts running again. The car accelerates normally while driving at higher speeds and does not stall or hesitate. I was thinking it might be an ignition problem or maybe the fuel pump. If someone can point me in the right direction the help would be greatly appreciated. Thanks Gerry.

[keiser31]

Need a little advice.

I have a 1963 Buick Wildcat 401 nailhead ( 33, 000 original miles) with a Rochester Carburetor. I just rebuilt the carburetor placed it on the car adjusted the dwell, set the ignition timing, adjusted the carburetor, and installed a new fuel filter. The enigine is smooth at idle, but when I accelerate from a stopped position at low speeds the engine just stops as if its not running and then either stalls or starts running again. The car accelerates normally while driving at higher speeds and does not stall or hesitate. I was thinking it might be an ignition problem or maybe the fuel pump. If someone can point me in the right direction the help would be greatly appreciated. Thanks Gerry.

I used to have a 1957 Chevy truck that did that very same thing. Almost drove me insane trying to figure it out. Turned out to be a small flake of rust (before the filter) that would sort of "close" like a door in the fuel line on acceleration. The truck would sit there and idle and I could even rev it up. It was not until I actually started to move down the road that it would "close" off the fuel line and stall. I guess it was the momentum of the truck. Cleaned that flake of rust out of the fuel line and it ran and drove like it should for many years after that.

[Guest kaycee]

Gerry,

You mentioned that you rebuilt the carburetor and also adjusted the dwell and timing. Did you also replace points and condensor? It sounds to me that if it runs good at high speeds it's probably not a fuel pump. I would check the carb. accelerator pump and setting and float level and drop settings, and make sure that the floats are aligned and free in the float bowl, and if you have'nt replaced the points, replace them and reset the timing.

kaycee

[gmdbhornet]

I did not replace the points or condenser. I did have a problem with the accelerator pump and I installed and replaced that as well as checked the float levels and drop. Still have the same problem.

Edited September 21, 2009 by gmdbhornet (see edit history)

[JZRIV]

From your post it seems the problem is only while driving the car. What happens when you open the throttle with the car in park? Does it do the same thing? If you start out driving and accelerate slowly, does it seem normal?

Maybe its a vacuum advance problem. It wouldn't hurt to make sure that is working properly.

Other than that if its fuel related, the accelerator pump would be suspect considering it seems fine in all but heavy acceleration. Check if you can see fuel squirting into the carb when you open the throttle with the engine off.

Did you have this problem before doing all the work?

[Guest doberman]

I aagree they said it all. But if it were me Id suspect the acc pump

and see if there was fuel squirting into the throtle body by looking down

in it as you open it up. of course with the engine off.

a lot of these carbs wont fill up the pump reservor if the flote is not set corectly.

alan

[Guest 1963Wildcat]

Need a little advice.

I have a 1963 Buick Wildcat 401 nailhead ( 33, 000 original miles) with a Rochester Carburetor. I just rebuilt the carburetor placed it on the car adjusted the dwell, set the ignition timing, adjusted the carburetor, and installed a new fuel filter. The enigine is smooth at idle, but when I accelerate from a stopped position at low speeds the engine just stops as if its not running and then either stalls or starts running again. The car accelerates normally while driving at higher speeds and does not stall or hesitate. I was thinking it might be an ignition problem or maybe the fuel pump. If someone can point me in the right direction the help would be greatly appreciated. Thanks Gerry.

Hey GMDBHornet-

I have a 63 Wildcat Hardtop in NC and have the EXACT SAME PROBLEM.

Jay Leno's Garage - 1963 Buick Wildcat

It seems to be more of an issue climbing hills..but occasionally is a problem on straight away acceleration.

It's like there is a "dead spot." My Rochester 4-barrel has been rebuilt and thoroughly

cleaned. The accelerator pump may have also been replaced with the carb rebuild.

Mine has 59,000 miles on the engine.

I was wondering if it may be a fuel delivery issue on these nailheads. Maybe the nailhead needs an electric fuel pump? Maybe it's the lower Octane fuel compared to early 60s?

E-mail some pics of your Wildcat to mackpro@gmail.com

Love to see them.

Jon in NC

63 Wildcat HT

[gmdbhornet]

Jason, Jon and Alan

When the throttle is opened when parked the issue does not happen. While accelerating slowly at low speeds between (20-30) is when it occurs. I changed the accelerator pump and I am getting a good squirt of gas in carb. Prior to rebuilding, the car would hesitate and chugg at all speeds (carb was dirty and inlet check ball was gummed up bad and had to soak for a while to losen). I did notice, while the car was running, the fuel filter (see through) was not full with gas and was percolating and would not stay full of gas. I am going to change out everything in the dist. and check the fuel line for debris. Thanks for everyones advice.

[keiser31]

Jason, Jon and Alan

When the throttle is opened when parked the issue does not happen. While accelerating slowly at low speeds between (20-30) is when it occurs. I changed the accelerator pump and I am getting a good squirt of gas in carb. Prior to rebuilding, the car would hesitate and chugg at all speeds (carb was dirty and inlet check ball was gummed up bad and had to soak for a while to losen). I did notice, while the car was running, the fuel filter (see through) was not full with gas and was percolating and would not stay full of gas. I am going to change out everything in the dist. and check the fuel line for debris. Thanks for everyones advice.

Mmmm...did you check for flakes of rust? It STILL sounds like the malady my '57 truck had. Especially after you said that the filter was not filling with gas. The very same thing occurred.

[sfair]

Those are CLASSIC symtoms of an inoperative or blocked heat riser. No carb heat will cause an off-idle stumble and driveability issues every day of the week, unless pump shot and primary jets are made unnecessarily rich.

[JohnD1956]

Had a similar situation on my 56. Turned out to be a leak at the base gasket of the carb. If you have the carb off again I'd recommend checking with a known straightedge to see if the base is flat.

[Chris Coon]

When you checked the accel. pump did you also make sure the check ball for the inlet to the pump was 'checking'?

[STuTZ693]

Replace the condensor and coil

[Guest wombvette]

You need to check the adjustment of the rear air flap and the associated rods and pull-offs. If that flap opens too fast, it will fall flat on its face.

[impala]

Also carefully re-check the accelerator pump adjustments. This is done with the idle screw backed out so the butterflies are closed. Then make sure the linkage is in the correct hole. A quick check in the Motors manual shows Buick using the center hole (if there are multiple holes).

Then take the measurement from the top of the air horn. The number varies depending on the carb number.

If not correct bend the linkage to adjust.

Since the accelerator pump does nothing at speed and if I'm reading right yours does fine there so it could be the cause of your low speed problems. You need to go through all the steps of troubleshooting that have been mentioned like checking for a vacuum leak, making sure the advance is working, etc.

BTW, I've never seen clear fuel filters that completely fill up.

impala

[gmdbhornet]

Jeff,

I adjusted the timing with the vacum advance connected. The manual does not say to disconnnect.

[Caballero2]

One possibility that no-one has addressed is that if the rotation of the breaker plate upon acceleration causes the points to short. (eg; frayed wire from the coil) It will act as though the ignition was turned off. A quick check will be to disconnect the vacuum advance, plug the line to the engine. Now, does it accelerate without dying? It may not even start.

Dan

'57-76C

'57-56R

'63-4467

[Guest 47jag]

I'm pretty sure you set the timing with the vacuum line disconnected.

Set up your timing light and watch the mark when you disconnect the hose. You will probably see it retard about 10 degrees. It shouldn't.

Another long shot is the vibration damper can separate. This has the effect of retarding the timing mark so that when you time to the mark it will be retarded. You can test this by power timing. Loosen the distributor, get help to rev the engine to about 2000rpm and advance the distributor slowly. The engine speed will rise if it is retarded. This is an approximate setting and it may have to be retarded slightly if it pings under load.

Art

[rocketraider]

4GC are notorious for acting weird if the wrong gaskets are used between throttle plate and float bowl. I'd check there first, esp if problem only surfaced after the carb rebuild.

Otherwise, I'd lean toward distributor advance.

[Guest cleaf30]

Any luck? I also have a 63 wildcat that' s doing the same thing except I haven't gone through it like you have. Where should I start?

Well I've started messing with it new fuel filter new pcv valve and checked the accelerator pump and the vacuum hose which were fine and noticed the exhaust manifold was cracked on the same side as the heat riser. Could not enough heat get to my carb and so that extra bit of gas from the accelerator pump not evaporate and then cause the car to bog. I also read somewhere if some valve got stuck it could crack the exhaust manifold. Is this true and if so what valve? I'll check the point gap as well but figured I'd throw that out there.

Thanks

Cody

Edited October 29, 2009 by cleaf30
Things happen (see edit history)

[gmdbhornet]

Well I finally got back to work on the 63 Wildcat and I appreciate everyones input. I wanted to update everyone on what I did and how it turned out.

- I completly overhauled the distributor and set the timing, dwell and idle speed.

- changed all the rubber fuel lines which attach to the fuel pump. (fuel filter now completly fills up and stays full)

- new plugs

After all was done the car runs great, idles properly and accelerates beautiful. As far as the hesitation it does it slightly when you give it gas when you pull out from a stopped position and at 20 mph. No way near what it did before. The only thing which is not attached is the heat stove pipe which attachs to the the exhaust manifold and the top of the carburetor. Its not attached because it broke off at the manifold and needs to be drilled out. I am not sure if that heat pipe has something to do with the hesitation. I would think its not heating the carb properly.

Thanks again for your input and any additional would be helpful.

Gerry

[F&J]

Is this pipe 1/4" or 5/16" and does it go to the round choke cover or choke body?

If so, that pipe heats a bi-metallic spring in the choke to make the choke open up. It will never run right if it is not hooked up. It should also have insulation on the pipe to keep it hot.

[gmdbhornet]

It does not go to the choke that one is installed. there is another metal pipe which goes to the manifold also and attaches to the top of the carb with a 5 inch piece of rubber hose.

[Guest kaycee]

Hi Gerry,

The tube you're referring to is for choke operation. It's actually a 'continuation' of the insulated tube that goes to the choke cap or housing. The one from the choke goes in the top of the manifold and the one to the top of the carb. air horn into the bottom of the manifold tube. Both tubes press into the slightly larger tube that goes through the exhaust manifold, so I'd run a drill through the manifold tube and get a piece of brake or fuel line tube the right size and just make a new tube for the one going to the top of the carb. air horn. It's just plain tubing with no fittings on it so it'll be a quick fix. Then just check your choke operation and adjust the choke if needed.

I still think your problem might be in the carburetor, so I'd double check the float level and drop, the pump adjustment (make sure the linkage is is in the right hole) and travel, and retorque the intake manifold and carb. bolts, and check all your vacuum hoses for leakage.

As was mentioned earlier, ignition should be timed with the vacuum advance hose off and blocked. Good luck!

kaycee

[Coley]

Gm had a bulletin back in the 60s that claimed a too wide a gap between the rotor tip and the dist cap could cause a slight hesitation on acceleration.

The fix was a new cap and rotor.

They also said to adjust (extend the rotor tip) by flattening it lightly.

[Guest sheffi81]

I have a similar problem (stall out on me but don't cut off). I have 85 ponti parisienne. I cranks my car early in the morning and idle great. When I drive and complete a stop and accelerate on the gas it hesitate. My carb has been rebuilt too. 4-BARREL Rochester carb

[Larry Schramm]

Just a thought to keep in mind. With many of us driving fuel injection cars we might tend to forget that there may be some hesitation on carburated vehicle which would be normal.

Vehicles with carburetors always had some hesitation because of the distance for the fuel to travel from the carburator to the combustion chamber.

This is especially true when the choke is transitioning from being on to off from cold start up.

If the accelerator pump is good and working properly and the vehicle does not stall, it might be working to its capability.

Edited January 29, 2011 by Larry Schramm (see edit history)

[carbking]

A couple of possibilities:

(1) Adjustment of the idle mixture control screws. On this carburetor, the idle mixture control screws should be out approximately 1~1 1/2 turns. Further out may cause "puddling" in the intake, which will cause a momentary "rich" stall on acceleration from a dead stop.

(2) Ethanol fuel. We suggest, if one is required to use ethanol laced fuel, one drills the idle tubes in the primary venturi cluster 0.002 inch oversize to compensate for the lack of energy in the ethanol.

Jon.

[carbking]

Just a thought to keep in mind. With many of us driving fuel injection cars we might tend to forget that there may be some hesitation on carburated vehicle which would be normal.

Vehicles with carburetors always had some hesitation because of the distance for the fuel to travel from the carburator to the combustion chamber.

This is especially true when the choke is transitioning from being on to off from cold start up.

If the accelerator pump is good and working properly and the vehicle does not stall, it might be working to its capability.

With all due respect:

I have been driving carbureted cars for 50 years. I have NEVER had one that was properly adjusted hesitate. The engine should deliver seamless power from idle to WOT. With a four barrel, if one can "feel" the secondaries engage, one needs to do more tuning.

Jon.

[Larry Schramm]

Jon,

You have a couple of years on me, but not many on driving vehicles. A carburated car will not perform the same way as a new port fuel injected vehicle. Some adjustments that cover some of the shortcomings of a carbureted vehicle may not allow the vehicle to meet emissions. There is a reason that all manufacturers switched from carburetors to fuel injection. Performance, emissions, fuel economy, etc. There are just a lot of variables and this is another one to think about...not to dismiss to keep looking.

[Guest mmikemitchell]

I don't know the history of this carburetor but here are some things to think about.

The 4G uses several different accelerator pumps and it is easy to get the wrong one installed. Did you use a good carburetor number to buy the carb kit? To test, look into the carburetor and open the throttle (engine off) a few times. You should see a good stream of gas squirting into the carb.

The gasket between the throttle body and float bowl can be the wrong one. Several with fit and kits usually have multiple gaskets to fit several models, but this usually acts as a vacuum leak and won't idle well.

There are a couple of float designs that sometimes get switched when replacing the float.

Also with a timing light be sure the timing marks advances when revving up the engine.

Food for thought.

Mike's Carburetor Parts

Edited January 30, 2011 by mmikemitchell (see edit history)