I just picked up an 1996 400 sport from a friend (cheap). the machine runs great for about 30 min. or until it gets hot then starts backfiring out the exhaust and no power. let it cool and your good for a little while again. I know he rode this with no battery around his yard for about a 1-2 summers with no problems. he replaced the cdi and external coil? not sure about that one. but does this sound like a stator problem ? or is there something cheaper I can try first. is there some type of thermal switch that can be shutting this down, due to no fan? I need to get a battery in this tommorow.

 

If it has a condensor or capacitor in the ignition, they can cause symptons like that when they heat up.

 

doesnt the cdi eliminate that?

 

anyone????

 

it does sound heat related for sure. not sure if theres an internal coil in the stator area you can check on or not. maybe someone w/ more knowledge could tell ya, or w/ a service manual.

 

anybody else??

 

What is the condition of your spark plug?
carboned up?