Engine Hesitation on Take Off - 1955

[D Yaros]

On take off from a dead stop there is a slight engine hesitation/stumble when stepping on the gas. We are talking a second or less. Then the car runs just fine. This condition is repeatable.

Had one place tell me it is a bad carburetor accelerator pump diaphragm; most likely caused by modern day ethanol laced fuel.

Problem with this theory, to me, is that I rebuilt the carb using an ethanol compatible kit from Daytona Parts Co.

Anyone else with this situation?

Is the likely culprit carb, vacuum, transmission, linkage or what? What do you guys think?

Need advice. Thanks.

[Marty Roth]

Sorry Dave, but from the sound of it, I would also make a first diagnosis as accelerator pump, but maybe there is something other than the diaphragm causing the hesitation.

[ronvb]

D Yaros,

Marty is probably correct but I also had a similar problem on an older Chevy and it was the mechanical choke rod that was binding after it was warmed up. I sprayed the choke coil in the manifold with WD-40 and it freed it up.

Juts my 2 cents worth,

ronvb

[Marty Roth]

Dave,

One way to check is to:

1. remove your air filter housing so that you can see into the carburetor, then

2. prop the choke open, again so you can see into the carburetor, then

3. manually operate the accelerator linkage to the carb, either with your hand, or by having someone step on the gas pedal

4. observe if you see a stream of gas "shoot" into the carb

If you see a shot of gas, then the accelerator pump diaphragm is probably not the problem, but if you do not see that stream of gas, then it appears to be the cause.

I once saw a case where the diaphragm was ok, but its linkage had failed ..

good luck,

and please let us know the results

[D Yaros]

Reporting back on this:

The hesitation is gone. The problem was the distributor vacuum advance. The arm on this advance was in a bind which prevented it from moving at all, let alone freely. Cleared the obstruction and all is well!