2001 yz 125 mid throttle miss?

My sons 01 yz 125 cuts out at mid throttle but as soon as he opens it up it runs like a champ... new to 2 strokes and clueless.. any ideas?

Is this a bike that you just bought?  If so...

 

-Check the compression, replace top end if needed

-Clean the Carb

-Let us know what the jetting is

-Are you running good gas, a quality pre-mix, mixed correctly?

 

If this is a bike that you've had for a while and it just started to run bad, it could be the same problem that I just found on mine.  The CDI went bad.  If you can, find another bike and swap parts to determine if this is your problem.

he just got the bike.. the previous owner rebuilt the motor top/bottom...  he runs 93 0ctane.. 32:1... amzoil dominator oil..  starts first or second kick every time...

Edited by rich1de2

he just got the bike.. the previous owner rebuilt the motor top/bottom... 

 

 

I have heard that one before :rolleyes:

Is this a bike that you just bought?  If so...

 

-Check the compression, replace top end if needed

-Clean the Carb

-Let us know what the jetting is

-Are you running good gas, a quality pre-mix, mixed correctly?

 

If this is a bike that you've had for a while and it just started to run bad, it could be the same problem that I just found on mine.  The CDI went bad.  If you can, find another bike and swap parts to determine if this is your problem.

 

took it to a shop

compression good...

cleaned carb...

rejetted it..

he seemed to think it was the CDI also so I got a used one off ebay... installed it... no change...

should I just try a new CDI or what?

 

 

Lean needle jet setting?

What elevation are you and, and what jets and needle position are you at?

 

For reference, mine is a 99 which I think is the same carb, I'm running:

 

350 Main Jet

37.5 Pilot Jet

Needle is in the second position from the top.

 

I'm at about 2,500'

 

My bike runs really good with this jetting, might be a touch lean, but I haven't had any problems yet.

 

Previous jetting was:

370 Main

50 Pilot

Needle in the 3rd position.

It would run fine with this jetting, but would have a slight stumble in the mid when the air filter got dirty towards the end of a ride.  It would also load up pretty bad if you let it idle.

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