Low speed/throttle Jetting Help

[KXRobert]

Ok, here are the specs of my bike and riding area....
'89 500
Good compression
No vacuum leaks that I am aware of
PC Platinum Pipe w/ Silencer
Uni Filter
V-Force Reed Cage
Sea Level
65-95 degree riding temps

I have jetted the carb to Paul's chart, (165 main, 58 pilot, 3rd clip, 2.5 turns out on air screw) and it runs awesome from around 1/5 throttle to WOT.  From idle to 1/5 throttle, it is running rough.  It sputters and feels like it is rich.  It also has spurts of revs on deceleration, which make it buck as you let off.  With it doing this, it takes a little longer to return to idle.  Back to the sputter, if I slowly crack open the throttle to 1/5 and higher, it cleans up and starts screaming.  I have been kind of ignoring it mostly because 2 strokes don't typically lug at low RPM and light throttle very well, however, I am begining to think it's a jetting issue.  I do a lot of trail riding which is getting annoying with the sputtery running conditions on the longer rides.  Would it be wise to go down on the pilot, or is this running condition kind of normal/expected being a 2 stroke?

[Paul]

The jetting chart is a starting place. The pilot jet is probably too big if it is sputtering down low. Go down one on the pilot jet and see what happens, the surging you are describing sounds like a lean condition and you should play with the air screw and see what happens. You could also move the needle UP one clip setting to richen it a little on the mid.

Also, the KX is not fond of fuel below 95 octane or so and ALOT of issues clear up when the bike gets fuel over 95 octane. I run two gals of 110 mixed to three gal of 92 and run it at 40:1 and the bike is a monster EVERYWHERE. I have a friend that dumps a can of Outlaw octane boost into his 5 gals of 92 and the bike runs well also.

[KXRobert]

That's what I was thinking of doing.  Do you know what the next smallest pilot is from 58?  I am guessing 55, but could be wrong.  The surging occurs when you let off the throttle completely at higher RPM and let it idle down...if a lean condition is causing this, I would assume closing the air screw would richen it up??  Wouldn't the inverse be true on my low throttle sputter?  If it is running this way b/c it's rich, closing the air screw would worsen this condition?  Or would you suggest that raising the needle would get a little more fuel into the motor before the throttle is closed, alowing it run richer on decel?  I wish jetting wasn't such a science.  I was able to get the jetting on my KFX 400 quad right on the first time around with my new pipe and filter.  Gotta love these 4 strokes when it comes to tuning.

Thanks!

[Paul]

Yep, 55 is the next smaller. I suggested raising the needle to richen it instead of closing the airscrew because the bike is running well everywhere else. Try a higher octane fuel while you are at it, might be surprised what happens

The jetting chart should get you in the ball park and with a jet size up or down, a .5 turn here or there, and a clip setting up or down you should be right on the money.

[sdkx500]

What is the jetting from the factory for the late model KX500's?  Maybe you could add that to your chart for a reference point.