Top 20 2003 Yamaha YZ 125 Questions & Answers

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.

Premixed fuel at a 30-1 ratio.

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.

Service manual says oil capacity is 19.4 oz. per leg which is 573.726 ml per leg. Be sure that you have drained all the old fork oil out first.

it should be just a bolt that goes through the base of kickstarter then wedge a screw driver into the slot to widen it and it should come off .but if you want to remove the shaft and all you will need to split the cases hope this helps

How does the compression feel now that you have it cranking over again. Without the decompression lever pulled in it should be next to impossible to kick it over. also, is there any noise coming from the engine (knocking, etc.) when you got it to start again.

hi there it sounds like the return spring is broken inside the cases this useally a sidecover off to replace it hopes this helps

this happened with my sons pw50 where the piston ring had snapped and when it locked it was stuck bewteen the piston & bore i would seek a shop or mechaninc to look at the top end and isnpect the piston & rings for wear or damage dont keep kicking as this could result in further damage

globe blown ?

check utube for wiring diag.

1). Confirm that the transmission is really in nuetral, or insure that the clutch is pulled in. 2). Have you tried removing the spark plug to insure that you do not have a hydraulic lock due to excess fuel in the cylinder? With spark plug removed, any excess fuel should be expelled out the open spark plug hole. CAUTION: INSURE THAT THE SPARK PLUG LEAD IS DISCONNECTED, AND HELD AWAY FROM THE OPEN CYLINDER TO PREVENT ACCIDENTAL IGNITION OF EXCESS FUEL.

check the timing marks are in line.

depending on the machine it is, this could be the AIR/FUEL screw it too lean.Often it is the AP (accelerator pump) on the carb. This has diaphragm and a pin. If this gets dirt in it it can cause erratic very fast idle, once revved or "bliped". Simply remove carb. On the bottom is the bowl, and another cover. Remove the bowl and this other cover and delicately cleam both. If diaphragm is dirty chances are bowl full of gunk too.

Change the oil inside check with your mechanic and choose a thicker oil.

As long as it is case oil and not an automotive oil for a car Because your dirt bike uses a wet clutch and some oills wil clog Up the friction plates

Does this happen when the bike is cold or hot? When a bike is cold and turned off, the oil in the gearbox 'sucks' the clutch plates together even when you disengage the lever. When an engine is warm and running the oil thins out, letting the clutch engage and disengage. Change your gearbox oil regularly to stop any sludge building up. Hope this helps..

TRANS HAS A WORN GEAR THAT IS WEARING UPON 2ND SHIFT

2001

Sounds like a selector rod has bent in the gearbox and the damage has got progressively worse by damaging the teeth on various gears. Drain the gearbox oil into a suitable container and look for any signs of metal particles or broken gear teeth. Firstly if you are not mechanically minded or don't have a repair manual and suitable tools then this is a job for the bike shop. This can be a very expensive repair. It can be more economical to fit a known good secondhand replacement engine, best o luck.