Jump to content
Sign in to follow this  

XR280R pilot screw jet/adj

Recommended Posts

91 XR with new 77mm piston 280 cc bore. Has stock PD05B Kehin. Main jet spot on with #125. Off idle & midrange too rich - misses & bogs. Will drop needle and retest.

It has a #40 "slow" jet. To check this circuit I set idle and slowly turn the pilot screw adjuster in (or out) to see if the idle RPM slowly rises. If i bottom the screw before it stops rising does that mean I need to go to the next size "slow" jet. If the screw is bottomed would that be richer (42) or leaner (37). The pilot screw adjusts air - right? So if I bottom out the screw (gently) I need a richer jet? and visa versa?

Also if full drop of the needle does not does not clear out the off idle/part throttle mid range - what are my options? Drop the main and recheck wide open or go to a different stlye (thicker) needle?

Share this post


Link to post
Share on other sites

What elevation are you at?

The pilot screw adjusts fuel on that carb.

It sounds like you need a smaller slow jet but #40 is awefully small for an XR250 already unless you're up in the mountains.

Getting the pilot set right should also clear up the part throttle issues.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...