Motorcycle Repair: Yamaha XT misfires at high speed when warm, hi chris, repair manual

Question
Hi Chris,
Ignition trouble with 82 XT550.  Starts easy,idles, runs perfect with lots of power until good and warm, then misses when accelerating hard.  After a short while, will start and run perfect again through all ranges until it warms up well then starts acting up again.  I'm suspecting the CDI or ignition Coil but have no way of testing under load. Had an XT550 parts bike, traded out the ignition coil and it acted the very same way. Realize could still be coil trouble as the old part was not proven good. Truly grateful for any help, Jody  

Answer
Hi Jody.
 Backfires are a product of valve and ignition timing, not the coils or the CDI box.  If it is overdue, the bike has been crashed/dropped, or if it was set wrong, then it will backfire.

Recheck the timing and valve gap in accordance with the repair manual.  Make sure that it is correct and the backfiring should be gone.

Good luck.
FALCON