Debbie
Check for a clogged up airbox...sounds like you have a mouse nest in it..I have evicted many a rodent family out of airboxes after bikes have been stored, especially if they have been stored in barns. I bought an XT600e last year that had almost a half pound of fresh Minnesota corn stored in it by a very busy field mouse all year...no joke..check to make sure your carb slide needle hasn't fallen off its clip... symptoms are identical, and although unlikely, make sure your main jet and main jet nozzles and air circuits in your venturi are clear. A bad coil can break up at higher RPMs as well, and a tired old spark plug can generate those specific performance failures. I would say timing is going to be just fine,assuming your pick up coil is good and securely fastened. Assuming your electrical connections are all clean and tight, the ignition components rarely fail.
You didn't mention what your spark plug looked like, but it sounds like you might be running with your choke on (I know you aren't). It sounds like you are either running fatter than a pig on top or starving for fuel on top, and checking those things out will reveal the problem. Try a new spark plug before you diagnose the other things. A bad spark plug will throw a dozen jokers into the deck and really throw you off base. A good spark plug will help you properly diagnose the problems and start eliminating possible causes.
Be sure and tell us what you found.
