One thing I will mention...when I was absorbed in the Rochester B and BC study a few years ago I learned that if your Rochester is straightened and sealing correctly and if the power piston is cleaned and polished smooth so that it moves freely in the bore then the amount of vacuum needed to lift it off the power valve can be as low as 7 pounds. The strength of the spring is the determinant and I found 4 different strengths of spring plus one more in my box of saved Rochester parts. Mostly the amount of vacuum needed was around 9, however. So you can understand how a working power circuit will function if you're driving using a good vacuum gauge. Step on the gas (say starting on a hill or passing another vehicle) and the vacuum drops to single digits and the power circuit kicks in and feeds more gas to the engine. Reach cruising speed on level ground and vacuum increases to where it stays (we'll say 14 for grins) and the power piston is off of the ball and the engine is only running off gas provided by the main jet. Going downhill of course will increase vacuum greatly. You can also appreciate what happens when one of these is driven infrequently and the ethanol gas causes the power piston to be firmly stuck in the down position.
During this I also tried adding tiny O-rings to the power piston (image below) and greasing the center section to help keep the thing from seizing in the bore due to the sticky gummy residue ethanol gas invariably leaves. And I tried the same thing with HDPE rings. I also tried making retainers and rubber boots to keep gas from being sloshed or sucked up into the power piston. These schemes sadly didn't work, but it was worth trying. I actually think the retainer and rubber boot idea would have the best chance of working, however there are some challenges to that and it might not be cheap to produce. I was searching for some way to either improve on the power piston or maybe even to remove it from inside the carburetor and put it outside where it couldn't be gummed up and might work more precisely and predictably...like the Carter YF does.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
