i just bought this fourwheeler about a month ago with new piston, rings, timing chain, cylinder, battery, gaskets, etc. ran great until the other day i was riding and started running ruff and then just quit and wouldnt start so we cleaned carb and everything and i kinda had a feeling it was my crank bearings.. well got it together and started and sounded ok but was kinda loud in the motor but it always was till i took off and right away started grinding and shut off and locked up.. if i roll it backwards itll come lose and turn over for a second then lock back up. pretty sure now its my crank bearings but i havent got it apart yet to see whas all rong..anyways i wanna know what the best mods are to get more power out of these it has an exhaust power up jet kit, were going to retard the exhaust cam and do the mod for the crank bearings so it doesnt starve it of oil..any otehr suggestions of what i should do? thinking about putting a stroker crank in it but ive heard it hurts them more then helps? anything you can think of let me know