250-500cc Help with a friends electrical/fuel problem

I good friend I ride with has a 1999 WR360 he bought used and it continues to foul plugs. He's an ex B enduro rider, so he rides pretty fast. We'll ride tight stuff at low rpms mixed with open trails where we can get the the rpms up and it'll last for about 45 minutes before it dies. We have to take the tank off to get to the plug and change it (he uses the Irridium plug) and it fires right up with a new plug every time. The plug coming out isn't soaked but it is running slightly rich (not tan) but he talked to Halls and has it jetted per their specs. Some people suggested the stator is intermittently bad, while others say the coil or the resistor. Any thoughts would be appreciated because he doesn't want to spend $ on a new stator (or rebuilt) and find out it's still not right.

Things I would check;
Float height, air screw adjustment, or crank seal.
Or it could be just too cold of a heat range, try one hotter.

Try a new coil lead,
They can fail once the engine heats up.
It might not be the plug,
It could be that the time taken to replace the plug is enough time to allow the coil lead to cool down until it becomes a useable resistance again.

i found the jetting on an iridium plug has to be absolutely spot on, i was fouling after every hour or so, i used a standard plug and it didnt foul to the point of stopping although was still rich.

I rejetted and havent had a problem,