The Stovebolt Site Forums The Shop Area Engine Shop Stumbling off idle

Fought with a 235 in a 53 one ton most of the day trying to get the stumble off idle cured. had rebuilt the Rochester carb, but couldn't get the engine to come off idle like I thought it should.

With breather off and engine off you could see a good stream of fuel when you moved the throttle. But only if you moved the throttle a good bit.

Finally figured out the holes in the throttle linkage and the link for the pump were worn. You could move the throttle plate a pretty good amount before the accelerator pump would move. Also the spring inside the well where the pump works would not return the pump to the top. Not quite strong enough. A stronger spring in the well helped return the accelerator pump to the to of it's travel, and though the links are worn some, this helped eliminate most of the slack.

Now when you goose it a little, it goes rather than falling on its face.

Who did the rebuild? The parts kit should include new accelerator pump parts and the manual shows the relationship between the linkage and the pump rod (you usually don't have to bend the rod unless to compensate for wear).

It was binding a bit, and I had another old B here that I used to help take care of the slack in the linkage. But the problem also was in the bore for the pump. Then with the new leather pump it wasn't returning as it should. A little bit more tension on the lower spring worked wonders.

Since it's running like it should now, I think I'll leave it like it is. Perhaps the old spring had lost some of its strength.

Most offidle stunmble is due to the transfer slot being overexposed. That easily happens if the idle is too high, the carbs calibration is to have enough blade angle so the engine will idle around 450rpmish and if the blades get angled greater (as with higher idle rpm)the transfer slot is overly exposed and you'll have a stumble.
Just sayin.