air/fuel screw

L

ldub128

Member

May 31, 2009

24

0

• Jul 7, 2009

• #1

Ive got a 1990 yz250 ive heard that the air/fuel screw should be 11/2 - 2 turns out. My bike seems to run alot better when i turn the screw out an extreme amount like 6 turns. Im turning the screw ccw. Its harder to start but runs alot better on top end when warm. Any reasons why this might occur? Thanks for any help in advance.

 

2

2strokerfun

Member

May 19, 2006

1,500

1

• Jul 7, 2009

• #2

You might need to go to a smaller pilot jet

 

L

ldub128

Member

May 31, 2009

24

0

• Jul 7, 2009

• Thread starter
• #3

Ok thanks. It has an ohlins big bore kit on it and im not sure if the previous owner messed with the jetting after putting the jug on so that could be it. Anyone know anywhere that i might be able to find the appropriate jets to run? Or is it just a trial and error thing?

 

High Lord Gomer

Poked with Sticks

Sep 26, 1999

11,788

35

• Jul 7, 2009

• #4

Your mixture should only be noticeably affected by the air screw and pilot jet from closed throttle up to about 1/4 throttle. After that, the needle and main jet have much more of an effect.

You're going about it in the right order, though. get the pilot jet and air screw properly set before moving on to the needle, clip position, and main jet.