[patrickt]

OK, I was helping another Holley 4160 owner recover from a dicey rebuild and lo and behold the Power Valve that came in the rebuild kit was opening and closing in the metering block almost like the diaphragm in a fuel pump. His vacuum, because of a larger cam, was a little lower than one might think, and the new PV opened at a number that was higher than it should, and that's where the two lines on the graph crossed -- making it open and close in rapid succession causing all sorts of goofy problems. Now, we didn't see the Ajax "white tornado" that we grew up with, but almost... with the engine hot and fuel percolating in to the venturis and "smoking" out. But, changing the PV, and setting the floats a little lower, solved all the problems. And the poor hot idle complaints that he had been enduring were fixed by setting the idle via the secondaries (by the secondary stop screw that you can get to with the proper tool, usually at least) and having the primary butterflies way down low below the transfer slot. I don't know if you ever had a problem with your idle being rich after the engine gets good and hot but, if you do, that's how you fix it. It's literally a magic trick for the 4160 and, if nobody ever tells you about it, you'd likely never guess it on your own.