intermitant problems are always unlimmited possibilities. what i would suggest is try to isolate the problem into one of three sections. engine, fuel, and ignition. stick a inductive timing light on the pto cylinder and get it to reinact the problem. if its an ignition problem the light should clearly cut out. this is sometimes hard to determine because the engine starting to bog may slow the pulses but may not indicate a loss of spark. leakdown testing of the motor is ideal but do compression tests when the motor is hot. a loss of temperature like that can indicate detonation. stator and timing sensors can seem fine when first started and can be subject to heat failure. i work at a cat dealer and have seen a couple instances where the wiering harness gets pinched under the tank just behinde the coils the wiers overlap eachother slide slightly under the tank then the tank flatens these wiers together creating a leak causing spark and timing issues. like i said too many possibilities to shout out and have you randomly looking everywhere at everything. like i said easiest way to figure it out is to isolate the system that is causing the problem.
