My 2003 yz 125 hesitates when you give it gas.It does it every time you switch gears.You have to give alot of gas to straighten it out.

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.

From my understanding the cable on the 125 is alot longer and where it connects to the carb. Its a different size.

I am presuming you are giving the gear lever a positive shifting motion when changing gears.
If the gear lever is completely tight on the gear shift shaft and the toe of the lever does not touch the engine sidecover when changing up, you may have a worn roller shift lever or loose screws holding this mechanism in place. See the exploded view diagrams of the SHIFT CAM and SHIFT FORK with all part names and numbers on the link below.
Cheers!

http://www.cmsnl.com/yamaha-yz125m1-2000_model10887/partslist/

Well - you will first have to buy an earlier model to get into 6th gear. The 2003 YZ 125 is a 5 speed transmission. There's nothing wrong with your bike.

85\90 transmission oil such as bel ray, motul or yamalube

If this problem only happens after starting the bike it will be your timing.

Check that your pickup coil is aligned correctly aprox 2mm BTDC and that the pick up wires are the correct way around.

If the timing is after TDC it can start the motor in reverse when kicking it over.

look to see if the clutch is burned out thats what happened to my ttr 125 and we change the clutch and it was fine then hope this helps

3 things,

carb check
float bowl check
and clutch check.

these, if not set right will give out what you are experiencing.

you may refer to the manual on the default / recommended settings depending on the type of gas you are using.

regards, safe trails.

Hey Ryan! Long time since hearing from you.

When you say "main clutch casing" do you mean the right side cover for the gearbox or do you mean the primary driven gear (AKA "clutch basket") that the clutch boss (AKA "clutch hub") and all the clutch plates fit into?

If you mean the right outer casing > they are slightly different, '97 pn 4JY-15431-10-00 and 2001 pn 4JY-15431-12-00. The entire clutch is the same from 1997 through 2001.

This is a shift fork or shift drum issue inside the transmission.


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