This 2003 yamaha yz 85 wont shift into gear whats wrong with it ?

SOURCE: Oil

drain the fuel, locate the float bowl drain screw, lowest screw on the carb and loosen it to drain the carb. replace the fuel with proper pre-mix, replace the spark plug and it should be fine

SOURCE: I have a 95 yz 125 head and 98 yz 125 bottom end.

You have a 50/50 chance that they will work okay. All the mounting holes need to line up and the cooling holes as well. Get a head gasket for the '98 and see if all lines up. Will the exhaust pipe fit the '95?

SOURCE: QUAD QUESTION! 1998 yamaha warrior 350 bogging down

I had a problem somewhat the same.

Make sure the air-intake boot has no holes in it.

SOURCE: 2007 yamaha ttr 125 wont go into gear. starts

gear selector may be jammed inside the casing or broken
check that the shifter is tight on the shaft!
check clutch adjustment
try rocking bike back n forth without using clutch while you try ******* the gear lever it may come unstuck
but get it looked at if it frees up!

SOURCE: when i kick my 85 yamaha yz 125 gas and oil come

Sounds like you have blown the exhaust gasket. Not a difficult repair .. just undo the exhaust manifold bolts and remove the exhaust. Purchase a new gasket and reassemble with the correct torque settings.