I do belive it is the one with the inverted mixture screw. I didn't know what that screw was for! I was looking at it this afternoon and scratching my head. The engine seems to run consistently (either rich or lean), it's just hard to get the transition smooth. Can you speak more about this "inverted mixture screw". What is it for and how does one go about adjusting it?
ORIGINAL: Waco Driver
Are you running the Perry Pump carb with the .375" venturi and the inverted mixture screw on the top left side of the carb? This pump did not run well with the standard Perry carb with a .315" venturi.
I ran the pump and Pump carb on an OS60 FGP Goldhead for a while. During the first couple of flights each day, the mixture would keep getting leaner & leaner and I would have to land and en-richen it a couple times each flight. After the second flight it would hold the setting. The problem was that the after run oil made the pump more efficient at first and when it was displaced by more running, the pressure would drop leaning the mixture.
I too gave up on the Perry carb & pump and reinstalled the original carb and backplate.