ok i lost half my speed and half power, i used to go 70 now i go maybe 30 and up hills,it barely makes it, also when id hit big jumps it would blow out a huge cloud of smoke often at times. i took it in to the shop and they told me i ran it low on oil, but didnt tell me what was wrong. can anyone help me and tell me what you think is wrong before i tear down the motor,its also a 2001 ive checked all the easy stuff and piston and rings looked fine

 

Well I'm sure you have it fixed by now but you will have to do a commpression check to know whats going on. Sounds like the compression is low should be at least 70psi to run.

 

It may be a carb problem, but if it isnt I recomend a top end rebuild, piston, rings, and valves and valve seats. How long has it been since you got it rebuilt? They say a 4 stroke should get a top end check/rebuild (if it needs it) every 40-50 hrs of riding time. From experience, I learnd the hard way that a Mojave will run with bad valves all the way till thay come through the head .