Gas pedal hard to push when warm
 

1965 GTO with restored Tri-Power. When the car warms up the gas pedal starts to get harder to push. Carbs restored in Dec 2021. They do have the phonilic spacers underneath. This is only when driving slow speeds on the center carb. Any ideas of what to check? Thanks. Chris

Look for swollen accelerator pump cup.

I’ll have a look. Thanks

Throttle shaft too tight in base, throttle arm too close to cast iron base, or accelerator pump cup swollen.

The throttle shaft needs to have .003" or more clearance to the bore, or it will stick when hot.

The throttle arm on the center carb (and the ends), needs to be at least 1/16" away from the cast iron. Iff too little clearance, when hot, the lever rubs on the cast iron base.

If the carbs were rebuilt with black (pre-ethanol) accelerator pump cups, that may be the problem.

I just had this happen after 6 passes at the strip. I'm pretty sure it is my accel pump. I have not touched this tripower in the 34 years I have owned it! It ran good so I never messed with it. Turns out the center carb still has a leather accel pump and it looks worn out. Pic attached...

If the accelerator pump cups are rubber, and still in the carbs, you may have a problem due to swelling of the rubber. If they are the original leather, I don't think they are the reason for the problem.

I posted in June, describing what may be the problem. Not likely, but if someone bumped the throttle shaft, pushing it either way so the linkage rubs on the cast iron base, this may be the issue. Visual inspection will tell you if this is it. If it is, as the base heats, the rubbing would get worse. Correcting it is as simple as using a flat punch and hammer, tapping the shaft to center each end so they don't rub.

Thanks for the tips! Now that I have the carbs apart, I found my center throttle shaft is worn pretty bad. It is likely the source of my issue as you suggested.