Check the spring tension on the points. It sounds like you're getting "point bounce" at high RPM, resulting in erratic ignition timing. If you're running some sort of aftermarket electronic ignition, all bets are off!
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!