My Yamaha Big Bear will idle but, when i give it some throttle it will sputter and pop and not run like it should. Put another new carb on it and it still runs bad. Changed the main jet to a larger and a smaller but not much change. Put new plug in and changed the coil out. Intake boot is okay. First carb seemed to burn leaner and the carb on it now burns a little richer. Valves are set right and timing marks are aligned and air filter is new. Almost left me in a hollow last week and barely made it back out. Missing and carrying on when i accelerated on a grade.

 

Does it only do this when warmed up? If so it could be the trigger or power coil on the stator going bad, could be that anyway. I am not a great believer in substitution as a way of fixing faults, Yamaha give resistance readings in the manual for both components, but this is not 100% accurate in my experience, so substitution may be the only option. Make sure all wires and connectors from alternator to CDI and CDI to coil are good first.