Check on the movement of the power valve plunger. It should move easily without any tendency to stick (although they usually stick in the rich position). If it's not opening the ball check valve as the manifold vacuum drops the mixture will be lean on acceleration.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!