If you are a two cycle owner you might stay with that, a high compression 4 stoke ie crf450r or CRF 450x they are in need on valve checking, and oil changes, high test (octane) fuel pump gas not race gas. Stay with the two stoke for less maintenance. If you want trouble free type use go with the honda XR 400 or XR 650 as they are bullit proof. In buying a used bike you may not know the condition it was taken care of, I recommend a NEW purchase if you in teh market for a hi compression CRF 450, Go with teh 450X and teh electric start for easy all around use. and if you in CAlif its green stickered. The R model is alot quicker in response like a two stoke and rev higher than the X , but since I ride away from a MX track teh X is a better machine.