Typically a seize will not turn over right away or at all. So it acts up, stuttering and stalls, and then starts right up? How does it run afterward? Absolutely you could have a coil heating up and failing, but normally the coil must cool before it sparks again. You have points on that bike? If so, how about the condenser? My experience with seizures is the piston sticks in the bore, suddenly. There have been times when a motor has tightened up and seized, It feels like someone is dragging you backward as you try to accelerate, You can tell by both the feel and sound that the motor is seizing. It doesn't sound like what you are describing to me. Definitely check electrical, if it has a condenser replace it unless it's new. It sounds like the plug is fouling but if that where the case it most likely would not restart so easily or at all. Did you float assembly have any liquid in them? If they are leaking it could effect the float level and richen it up, Just throwing stuff out there, hope something helps.
1993 XR650L; 14T CS, Dave's carb mod, Modified stk muffler, Airbox Mod, Battery relocation, Bar risers, Uni filter, No passenger pegs(to make it super lite), Blue powerband.