I have worked on 2 & 4 Stroke engines for many years but I could use a little input on this problem.
A friend of mine brought me his Quadmaster after the local dealership couldn't fix his problem (after $988.00 later) , The ATV starts & idles fine but at mid throttle the ATV bogs. This only happens when the engine is under a load (accelerating beyond mid throttle). On a stand and in gear or neutral it revs normally at all throttle positions, but when on flat ground under the load of it 's own weight + rider it bogs @ mid throttle ( 22mph.). The fuel circuit checks out & the carb has a new diaphram/slide plus a new coil & new plug & fresh gas. The fuel screw has been adjusted properly so the only other things I suspect is a minor short (plug connector or wiring ),Timing or Magneto gap setting.

I would appreciate any viable input to this problem. Thanks , Buzz

 

i had about the same problem with an arctic cat 250 i had, turns out the valves were shot.