Sticking carburetor

[Ellis Kinney]

1981 Ford, F-100, 300 inch six cylinder. The carburetor is hanging up at an idle. For instance, sitting at a stop light, when I depress the gas pedal there is a catch before I can accelerate, which causes the truck to jump. This happens on a warm engine only. The truck runs fine for the first half hour. It is not in the linkage. The other thing is, this has happened on multiple carburetors. Suggestions??? Thanks, Ellis

 

[DaveBN]

Take one of the carburetors to a rebuild shop. I suspect one of the internal components is sticking. If you don't know of a local rebuild shop ask someone who races at a local track, they will know.
Are you SURE it's not the linkage? Does it have an external control for the choke butterfly? Maybe that's your problem.
Dave

 

[Geo-TH,In]

1981 Ford, F-100, 300 inch six cylinder. The carburetor is hanging up at an idle. For instance, sitting at a stop light, when I depress the gas pedal there is a catch before I can accelerate, which causes the truck to jump. This happens on a warm engine only. The truck runs fine for the first half hour. It is not in the linkage. The other thing is, this has happened on multiple carburetors. Suggestions??? Thanks, Ellis

If I recall there is an accelerator pump that squirts gasoline in the carb when you depress the gas pedal. .
With the truck now running, remove the air filter and look inside the carb for gas when someone pushes on the gas pedal.
The accelerator pump is like a squirt gun spraying raw gas in the carb.
If the engine is warmed up there shouldn't be any choke. The gismo that removes some of the choke when it is cold. It is vacuum operated and I called it a choke pull off.
Good luck finding anyone who rebuilds carbs.

 

[DanielW]

When you say, "this happened on multiple carburetors", that makes me think the problem may be in the pedal/linkage. When you say, "the problem is not in the linkage", do you mean just the linkage at the carb? Have you looked/checked everything from the pedal onwards? It could be something as foolish as the pedal pivot hinge catching when foot pressure is on it (I mention that because I had exactly that happen in an old Fiat 850).

I'd be looking pretty intently at all those before I looked at the carb again if you've tried it with multiple carbs with the same result. Do you notice the same problem when you disconnect the linkage from the pedal and rev it up from under the engine by operating the carb manually?

The only other thing that jumps to mind (presuming it's not the carb, which I kind of doubt if multiple carbs have had the same issue) is some problem with the timing/advance of the dizzy. Maybe try advancing & retarding it a smidge to see if it helps/hurts. Or could be something up with the ignition components inside the dizzy, which can cause all manner of wacky issues.

 

[rustred]

1981 Ford, F-100, 300 inch six cylinder. The carburetor is hanging up at an idle. For instance, sitting at a stop light, when I depress the gas pedal there is a catch before I can accelerate, which causes the truck to jump. This happens on a warm engine only. The truck runs fine for the first half hour. It is not in the linkage. The other thing is, this has happened on multiple carburetors. Suggestions??? Thanks, Ellis

I am not understanding your wording , “ hanging up at idle” or a “catch before I can accelerate .”are u talking about a hesitation ??

 

[rockcreek4630]

1981 Ford, F-100, 300 inch six cylinder. The carburetor is hanging up at an idle. For instance, sitting at a stop light, when I depress the gas pedal there is a catch before I can accelerate, which causes the truck to jump. This happens on a warm engine only. The truck runs fine for the first half hour. It is not in the linkage. The other thing is, this has happened on multiple carburetors. Suggestions??? Thanks, Ellis

Does that one have the spacer between the carb and manifold it could be making the base of the carb distort when hot making the butterfly stick.

 

[Ellis Kinney]

Does that one have the spacer between the carb and manifold it could be making the base of the carb distort when hot making the butterfly stick.

Yes it does. I think it has something to do with primitive pollution control.

 

[Ellis Kinney]

I am not understanding your wording , “ hanging up at idle” or a “catch before I can accelerate .”are u talking about a hesitation ??

Not a hesitation, but a catch.

 

[used red MN]

Not a hesitation, but a catch.

I am almost certain that vintage of truck was using a cable between the pedal and the carb throttle lever. They tend to become dry and sticky. You can try to lube it. Disconnect the inner pull cable and the housing from the carb and then raise it up so gravity will pull the lube down into the cable housing. May have to pop a dust cap off of the cable end of the housing to allow better access to to get lube in there. Use something a bit better than WD40, spray it in there as you move it back and forth.

 

[rustred]

Not a hesitation, but a catch.

I have never heard that explanation in 50 years of working on carbs. So it’s not like catching a fish then.

 

[scootergmc]

Warm it up, disconnect the linkage, open throttle at carb by hand. Is it stuck? Issue still present? If so, yep, it's somewhere on the carb/plate.

However linkage/cable/pedal obstruction is far more likely.

 

[Janicholson]

Use spray on (with straw) chain lube. it goes on rather fluid and ends up a higher viscosity oil when an hour goes by. I agree with those that indicate the need to check the linkage separately from the carb. Some from that vintage have Idle stop position systems that control cold run Idle. they can provide a sticking point if worn, and might not be part of a replacement carb. Jim

 

[timcasbolt]

Sounds like there are multiple ways to describe a symptom. In my world, you're talking about an off-idle stumble, which is usually an accelerator pump problem. Either linkage out of adjustment or needing a new pump.

Also, because of the age, it's wise to do a thorough inspection of all vacuum lines and sources.