Not sure if anyone is still having this issue but I was having the same problem recently on my 98 TRX300. Turns out the guy I bought it from must have replaced the starter at some point and put in the wrong one. The starter that was in the machine was spinning clockwise which had the starter gear spinning counterclockwise and not engaging the one way bearing. I happened to notice the arrow on the flywheel showed clockwise direction while the starter was trying to turn the motor CCW. I just ordered and put in a new CCW starter and the machine fired up right away for the first time since I bought it. Check your flywheel direction and make sure the right starter is installed. Hope this helps someone!