Don,

I have been following this thread with some interest because I have had similar problems.  I have gone through most of the steps that you have gone through and gotten similar results.  I have added a fuel pressure regulator to my plane to limit the fuel pressure to 4 psi.  This didn't help very much.  One thing that I did find is that the arm, where it pushes up against the needle had worn a down significantly.  I replaced the arm, but still have problems, just not as often as I did before.  I also noticed that only the carb that was causing problems was worn.  I'm not sure why that carb would be subjected to more vibration than the other, but the worn spot on the arm would indicate that it is shaking more than the other.  Just a couple extra cents to through in the pot to think about.

Jim Rieck