20 Most Recent 2003 Yamaha YZ 125 - Page 6 Questions & Answers

excessive piston clearance.really needed bore job with oversized piston,not just honed and rings.measure piston to cylinder clearance,check spcifications and verify

Premixed fuel at a 30-1 ratio.

No oil goes into the crank case as it is a 2 stroke. The oil is premixed in the fuel at a 30-1 ratio. The gear box takes 10w-30 se oil.

The clutch and gearbox share the same oil. The oil for the motor is 10w40. Stick with the major brands; Pennzoil, Quaker State, Mobil, Yamalube or Shell.

look on the engine, there will be marking on it for the 'cc' if a yz80 it will prob be '79cc' and if yz85 it will prob be '84cc'

check utube for wiring diag.

If it does stay in gear when barely throttled but does not stay in while under load, the engagement dogs on the gears(inside the engine) are bad and the engine will need to come apart to repair it.

wear or play on the gear selector drum,could even be the gear selector plate on the end of the drum is loose its star shaped with a central bolt or screw,check the locator spring also.