I would have to say try the compression test and if thats good, I would have to say it's something electrical you say you have spark but if its not strong enough it won't do the job...and these electrical things are (1)the spark plug/ignition coil and/or (2) the coil pickup which is inside the stator cover.....and possibly but doubt the CDI unit.


later
Superstar

Get an OHM meter and check your results with the specs in the repair manual on the wiring that deals with the ignition....Hope this helps ya out

 

yamaha guys get the heck out, (put politely), if ure not going to help.