Its actually very easy, take apart the gearbox being careful to place your parts on a towel in order so u can get it back together. It helps to have a good light and a magnifying glass. Just take each gear and inspect the teeth, if u see a burr or a rough spot, just use a very fine file on it, and go lightly, u dont wanna weaken them anymore, just clean them up. And be sure to wash everything, let dry and lube it lightly before putting it back together. Cut a strip of paper (regular notebook type) put it between the clutch bell gear and spur gear or gears whichever the case may be. slide the motor towards the spur gear until u can just rotate the gears with the paper on them. If the paper binds it up, it is too tight. Be sure to keep the motor square in the ounts also. And keep an eye on the screw, cuz if they get loose, goodbye spur gears. I not only did mt clutch and spur gears, I also did this to my front and rear diffs. Still need my parts, but i got the other ones epoxied, Im ordering the new ones tonight and Ill be able to give the fixed ones a run tomorrow. Look out stop sign, Here I come. Oh, and the low speed mixture screw is on the side of the carb, iti is encircled by the throttle levers housing.