I rebuilt my model 59 carburetor and adjusting the idle mixture screws all the way in or all the way out changes nothing. The engine is idling rich (black smoke from both exhausts). I know the first thought is blocked or restricted internal passages. I have been through this carb 3 times now and there are no blocked passages. Any ideas??
Could be wrong gasket on the power valve (or late model PV and its leaking fuel, ^ should be running around 3 PSI fuel pressure. the Power valve should have a flat face with NO taper where the gasket sits. If it has a taper it will not full seat and leak. There is a thick gasket that will seal this type of power valve in a 94/59 carb
The carb kits I bought came from NAPA. The kits had 2 power valves. I installed the one that looked the closest to the one removed when I initially rebuilt the carb. I've been reading some articles on power valves and found there are different ones identified by a specific number. My flathead is basically stock except for being bored .030 over. How would I know which power valve to install when the ones in the kits have no numbers stamped on them? I don't know what my fuel pressure is, but I will be installing a fuel pressure gauge soon to find out.
Usually 7.5 power valve for stock, single carb. Number (usually) stamped on the side. Spring tension is the difference in different PVs. (From what I can see) Also different styles of PVs that do and don't fit. Sometimes the sealing washers don't seal, as mentioned in post 3.
"The carb kits I bought came from NAPA. The kits had 2 power valves. I installed the one that looked the closest to the one removed when I initially rebuilt the carb." Is it possible that you got one power valve and one spark valve? The easy way to tell the difference is that the plunger on the power valve may be pushed in, but the plunger on the spark valve may be pulled. Jon.
I think you are right on that. Although the valves look similar, one can be pushed in and the other has to be pulled out. Thanks!!
I went through my new and used parts. I found one used power valve with 7.5 stamped on it. It had 2 gaskets on it. One is soft metal and appears to be lead. I cleaned the valve up and installed it in the carburetor (with both gaskets). Result: I can now adjust the idle mixture screws; no more black smoke from the exhaust and I think it has solved my problem of gas leaking into the crankcase and diluting the oil. Today I changed the oil for the 4th time and the truck hasn't even seen the road yet!! Thanks for all the input!
If the power valve has been sitting around for a while the rubber may be close to perishing. It would still pay to put a new one in.
You're right, Clem. That is something I will do prior to this thing getting on the road. At least I know now how to solve the problems I was having. Thanks!!
Agree with above. If you find no changes when tightening up your idle screws normally you have a vacuum leak. Sent from my iPhone using The H.A.M.B. mobile app
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