VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 216 hesitation after carb rebuild

1940 with 1953 216 and Rochester carb with hesitation upon sharp acceleration.

My engine was running great but had excessive black soot out exhaust. My friend removed carb for rebuild/cleaning, although it was very clean to start with. The gent at CarbJunkies (great folks) suggested the vacuum piston may be hung-up, not that the Jet (51) was too large. The good gent at CarbJunkies thought 51 was actually on the lean side. Sure enough the vacuum piston was bound up. The base gasket is proper, having the 4 slots to allow vacuum to the carb. My friend re-installed the now super clean carb, with new accelerator pump cup and free vacuum piston. He also removed 2 sparkplugs, and neither was near as black as expected, some black around the perimeter, but center was tan’ish.

Upon driving now, it hesitates on hard acceleration, but once the rpm is established, pulls good.

Thoughts as to what might be causing the hesitation?? The distributor was not touched during all this carb work. Car has had Pertronix on for as long as I have owned it. Appreciate any suggestions.

Is the manifold heat riser free and working?
Problem could be ball check in accelerator pump or check balls in pump circuit.You wiill beable to hear the check ball in the pump rattle when you shake it.
The correct check balls. one aluminum and one steel should be correctly nstalled according to the Carb ,year and number.
The #51 jet is correct.
The hesitation problem was being covered up by the rich mixture caused by the sticking power piston.

Gene, thanks very much for the advice. We'll have to get back into the carb and see what we find with the check balls.

Gene, sorry, I should have said on earlier replay that there is no heat riser...my model is hand choke, if that makes a difference. Regards.

There should be a heat riser as well as a choke.

The heat riser is in the exhaust manifold just below the carburetor.

And it is contolled by a thermostaic spring

Ahhh, thanks for that. Will need to investigate. Meantime, top is off the carburetor and the new accelerator pump cup is swollen and a bit sticky to the touch, not moving freely. Not sure why given it is new, perhaps contaminated with something or the wrong cop? But needs to be changed, I think. Will learn more on the heat riser but it seems the cup is most likely the problem with vehicle hesitation upon acceleration.


Please advise any other guidance that comes to mind, much appreciated.

The carburtor kits come with two different cover gaskets, One for the original low cover Rochesters and one for the replacement high cover jobs.........

Reporting back: First the good news. Carb is back together with replacement accelerator pump cup and works very well, not a trace of hesitation, easy cold and warm engine starting and car running well at all speeds. Not so good news: Located heat riser but not functioning as spring is missing. Mechanism appears to be stuck in closed position, so that remains to be addressed. However, so far, car is running great without it. But here in Virginia early Spring temps range from high 40s to 60s these days so perhaps non-performing riser will present engine performance issues in colder weather....although I rarely take the car out in winter. Anyways, thankful the carb is now functioning well.

There are lots of posts over the years about “unsticking” heat risers. Patience and some type of penetrating oil are the secrets to success.

The method that seems to work the most is to liberally soak the ends of the shaft with the penetrating oil for quite a few days. Heat cycling it might help. Some people used a torch to heat the area.

Gently tap on the shaft to try to make it move back and forth in the manifold. You might need to do this over several days. It can only move a small distance due to the butterfly plate on the inside.

Trying to open it with vise grips on the shaft will pretty much guarantee that you will be removing the manifold for a more complete replacement type repair. The shaft is not very strong and will twist off easily.

In cases when things are really frozen you will have to remove the manifolds and work at it from inside where the valve operates.

It depends as to what position it is stuck in.
If it is in the warmed up position no problem except for some possible hesitation when cold.
If i the cold position it is heating the passage under the carburetor making the carburetor and the fuel in it hotter than desired leading to spilling over when hot and difficult restarting, etc.

Gene, fortunately, stuck in the warmed-up position I believe. Rusty, thanks for the guidance on feeing up the riser. Especially the part of patience and not trying a lot of force. Thanks to all.