Ed if it is a Rochester B, there is a good chance the problem lies with the power piston/power valve. Now having said that, it is a VERY good chance you have warped castings and therefore you can't have enough internal vacuum to lift the power piston off of the power valve ball. Please don't try to sand the castings flat. There were little ridges cast into the float bowl and air horn that were meant to help seal the gasket. There are only 4 screws holding the top of this carburetor on, and once those ridges are gone, the likelihood your gasket will ever seal the float bowl to the air horn becomes notably lower. Please also don't try to solve this problem with 2 gaskets...it will only make it worse. If you used one of the cheap kits rebuilding it and if you followed the instructions in that kit, this could be contributing to your trouble in ways you might not expect. The fuel inlet orifice in the seat is possibly too large...maybe as large as .110" in diameter. I found 3 different sizes in the ones I dissected and they ranged from around .075" to around .110". Too large and your fuel pump's output will outrun your float/needle/seat's ability to regulate things. In plain talk, your pump will push gas into the float bowl faster than your carburetor can regulate it. You'll run very rich, because you'll have too much fuel in the bowl all the time. Power piston not working or don't have enough vacuum to keep it off the power valve ball? In that case, the power valve will be open and you'll be running too rich. How about the float setting? There were something like 140 different models of this carburetor made. From what I've learned there could be numerous different float setting measurements and the difference between some of them could be as little as 1/32 inch. The instructions in your cheap kit will tell you to use something like 1 9/16" no matter which model you have.
About 3 years ago I showed everyone here how to straighten the Rochester B or BC castings using one small and simple piece of 3/8" steel and a gas BBQ grill. I don't think I could have made that task any easier. I also studied (using a handheld vacuum pump and gauge) the power piston springs. There were 4 different strengths of springs I found in the guinea pig carburetors I purchased for the study. Some of them would allow the piston to lift at around 9 inches of vacuum and a couple required more like 14 inches. If you are losing vacuum due to warped castings, there's little hope you will have 14 inches of vacuum at the top of that piston, so your carburetor will never run as it was designed. That study is still here. I expected it might have become a tech tip, but for whatever reason it didn't.
Having added these hints, have you ever considered purchasing a Carter YF carburetor? Or maybe a Zenith 228? I know some people think a Rochester B is a miraculous design and I tried very hard to keep an open and optimistic mind during the study, but a sow's ear is at the end of the day still a sow's ear.
