Is this thing doomed?

[jeremy dronen]

I recently bought a motorized bike 80cc and with a few adjustments, it ran great for a few days. Then it started running oddly. Remember how carburated cars with a bad accelerator pump run? too much throttle and they want to stall, too little, they want to stall, you have to constantly feather between the two until it smooths out... That's what it was doing, now it does nothing. good spark, plenty of fuel, sounds great otherwise, but not freaking starting anymore.
Tonight I plan to remove the exhaust and try again, and if that doesn't work, i will try the new CDI and if that don't work... what?!?

 

[crassius]

next, one would look for things that are getting loose from vibration - gaskets, motor mounts, wire connections