I'm wrenching on a 1993 Safarie Rally 500 fan cooled.

The sled goes into a bogging condition after about 5 minutes +or- of run time.
Whatever is doing this is heat related.
Here's what I've done so far:

-cleaned carbs
-new plugs
-swapped CDI and voltage regulator from a indentical running sled,no change
-checked every wire connection

I determined it's not a fuel problem by holding the throttle while it's bogging and pulling the fuel lines off each carb and it's pumping fuel. Also added fuel with the primer with no change.
While its bogging the lights do not change and remain nice and bright, hand warmers are hot.
While bogging its hitting on both holes, stronger on the mag side.

Is there two parts to the stator? Lighting and ignition???

Sounds like a head gasket or coil to me. If it runs great while the engine is cool, and youre sure the engine is getting gas, then the only thing i can think of is head gasket or coil. Ive seen the coil get hot and start quiting and also the head gasket start leaking. Hope that gives you a place to start.

Are they Tilson or Mikuni carbs, If they are Tilson, check they diaphrams in your carbs. I had they same problem on an old Yamaha, and it turned out to be a perferated diaphram in he carb
Hope thios helps