Rough idle on 1951 8BA

[51shoeboxer]

Originally Posted by Steve51

Leaking power valve in the carb base or poor mating surface in the power valve chamber where the carb sits on the base causing a vaccum leak. Some of the new valves don't seat properly without a slight modification.

I think you are right. I saw a video that demonstrates how the gasket under the power valve might get hooked on a ledge on the power valve and cause a vacuum leak. I couldn't check for that, but with the engine running, I shot some carburetor cleaner on the gasket for the power valve chamber and on the vacuum connectios on the carburetor and the vacuum chamber; and saw no difference in the idle quality. I guess I'll have to pull the carburetor apart.

[scicala]

Originally Posted by 51shoeboxer

I think you are right. I saw a video that demonstrates how the gasket under the power valve might get hooked on a ledge on the power valve and cause a vacuum leak. I couldn't check for that, but with the engine running, I shot some carburetor cleaner on the gasket for the power valve chamber and on the vacuum connectios on the carburetor and the vacuum chamber; and saw no difference in the idle quality. I guess I'll have to pull the carburetor apart.

When you seperate the base from the bowl, if it's wet with fuel on the vacuum side of the power valve, that petty much says a ruptured PV diaphragm.

Sal

[40ford]

Originally Posted by 51shoeboxer

I think you are right. I saw a video that demonstrates how the gasket under the power valve might get hooked on a ledge on the power valve and cause a vacuum leak. I couldn't check for that, but with the engine running, I shot some carburetor cleaner on the gasket for the power valve chamber and on the vacuum connectios on the carburetor and the vacuum chamber; and saw no difference in the idle quality. I guess I'll have to pull the carburetor apart.

Did you try what I suggested before you pull the carb apart?I realize you sprayed carb cleaner in ports but compressed air will thoroughly clean them.

[Steve51]

There are a few sellers who have the modified power valves. I rebuilt my carb after having this same issue but my kit had the poor fitting power valve. I used a small sharp edge file to square off that rounded area on the valve that causes it not to seat properly. I also just disconnected my non functioning wipers and hooked up a vaccum gauge under the hood. Its temporary till I get around to dealing with the wipers but its a great diagnostic tool.

[Steve51]

Originally Posted by 51shoeboxer

I think you are right. I saw a video that demonstrates how the gasket under the power valve might get hooked on a ledge on the power valve and cause a vacuum leak. I couldn't check for that, but with the engine running, I shot some carburetor cleaner on the gasket for the power valve chamber and on the vacuum connectios on the carburetor and the vacuum chamber; and saw no difference in the idle quality. I guess I'll have to pull the carburetor apart.

This may be unlikely as you say it ran fine for 80 miles. I also found my carb was missing the check weight that goes in the hole between the towers where spray nozzles sits. The check ball in the accel pump was also stuck. Along with the leaky power valve it ran very rough. Since it sounds like you are going into the carb just make sure all the parts and little gaskets are there in place. I also used 220 and 400 grit sandpaper on a flat surface to get a better fit on the the carb and throttle plate mating surface. Before I started I could see slivers of light between them held metal to metal.