My brother's 200 moto4 works pretty good most of the time but occasionally it will have a burst of power for a short time (maybe a couple minutes) that will actually sit you back on your seat but it never lasts. He can usually barely keep up with my 300 Bayou on a long flat stretch but when it has it's power burst he can easily leave me in the dust. It always happens after an hour or more of driving.
Any ideas what could be causing it? It would be nice to have it working this good all the time.

 

I,d start with a carb cleaning and spark plug change and see what happens. change the fuel filter if it has one.
I had 1987 240 Moto4 and it ran great and only could do 40 or 45mph on the best days.
I don,t know if a Moto4 had a rev limiter but if it does it sounds like its acting up and letting the 200 scream out when it should not be. Fun but not good in the long run.