Check the points to make sure they have enough spring tension. Some brands of points have a copper conductor strip, and a steel spring that can get misplaced. Without the steel spring, the engine will idle, but the points start bouncing and messing up the ignition timing at higher speeds. A bad condenser can also cause the same kind of problems, and they're notorious for being bad right out of the box.
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!