I have a 1999 Polaris 335 Sportsman that won't rev up past 3 to 4000 RPM's and starts sputtering the more throttle you give it. Engine starts good cold runs and idles fine down low RPM and even has good throttle response right off idle. First thing, tried a new plug. no change. Tested fuel pump and output seams to be adiquit Can hear the carb opening up the more throttle you give it (the slide is opening up and not sticking, i overhauled the carb but did not see anything obvious but the carb was not very dirty inside anyway. And this was with air cleaner fully assembled or not.) Moving on to other possibilities. I checked the spark and timing and both are OK. Not losing spark at higher RPM and timing is advancing to spec as it should.
Removed muffler to eliminate possible plugged exhaust. Checked valve clearance, cam lobes for ware and for weak or broken valve springs and correct cam to crank timing, all OK.
Checked engine compression, around 40psi. That seems too low to me but didn't
have spec. Performed cylinder leakage test and was good, less than 10%.

 

Pull the black wire from the reverse limiter on the terminal board and see if that helps. Item #36.