Ok, onto secondary possible culprits.
Idle adjustment screwed - I think we can discount that one, check to make sure, of course.
Throttle adujstment too slack - too slack and your throttle cable might actually not be holding open enough to keep sufficient fuel moving to sustain combustion.
Plug gap misadjusted - shorten it a hair and see if that helps.
Timing off - If it's a CDI, I dunno....but if it's points, adjust the timing a bit.
Do these one at a time so ya know which one fixes the problem, mind.