My Dads Big Bear 350 will run for about 30 minutes then backfire and die, after it cools down it will start run for awhilethen do it again, any ideas?

 

Check carb and tank vent tubes. When dead, do you get spark from plug?. If no spark, change plug and check ignition circuit. If you get spark, check carb float bowl for fuel, carb float could be sticking or float fuel inlet clogged; causing float bowl to run dry.

 

He has replaced coil,plug, spark plug wire checked all carburation . It seems to be a heat electrical thing. Maybe a faulty thermo switch?

 

Have stator and stator pickup tested, it could be overheating and shorting out. A competent motorcycle shop can probably test it for you, if your dealer can't.