Be careful when setting timing "to the ball". Some balls represent 5 BTDC which is a fine starting point for timing. Others denote 2 ATDC (which is the case with my flywheel). I have found the engine runs best between 8 and 10 BTDC on 87 octane 10% ethanol fuel. Not sure how prevalent the 2 ATDC ball flywheel is......
As for the power piston, I use a handheld vacuum pump with a conical tip. With the carb apart and holding in proper orientation I make sure 10"mercury will move the piston. It will not stay due to leakage around piston, but you will see it pull up.
As for diagnosing a rich running condition from power valve, I found the mixture screw will be about 1 1/2T out at about 500rpm for a proper idle mixture +/- 1/2 T. If it falls outside of this range I look for leaks if on the lean side and check power piston if on the rich side. This of course assumes carb is thoroughly clean.
