Jetting!!! Again and again and again!

[mikesmith]

Good advice.

[kawdude]

How do i tell if the airscrew is ok?

[gowen]

as in position? or the actual screw is bad?

I've always done this by the idle, I screw it out or in, whichever gives the best/most idle.

[kawdude]

Is the most/best idle where the screw should be set?  If this is out past 1.5 turns the slow needs to be lowered one size.

[gowen]

Kawdude, to my knowledge you are suppose to keep going down until you get the highest idle. I'm at a 42 pilot and going down, I'm thinking a 40 is my next stop. Cause I'm at 2.5 turns and still have a struggling idle.

I was at the 1st notch on the needle, but ended up being REAL lean on the mid. I'm at the 2nd and seems great in the mid, but the top is still a VERY  little rich on the top.

But, still have problems down low, I'm hoping to take care of the low-end and move to the 3rd notch in the mid.

[kawdude]

Right now I have mine sitting at the bottom notch.  It's very rich mid and up.  I'm going to move it back to the 2nd or 3rd notch to lean it out.  I may try going down on the slow jet because the screw still doesn't do much to change the idle.

[gowen]

Kawdude, if you mean the bottom notch being the 5th notch, that would VERY much effect the idle and top-end performance. I'd drop it to the 2nd notch right away and see the performance change, I promise it will help ALOT. That was my problem was the needle, once I got the needle to the 1ST notch it helped me realize where the circut was off, and I was able to lean out the pilot and main slowly, once I got down in the pilot, I was able to move the needle down one (richer 2nd notch) and that has helped alot. I'm just about right in the mid section and top, a little rich on the top when in humidity/rain. I'd adjust the needle and give it a try. Let me know.

EDIT: I forgot to mention that when I sent the needle to the 1st notch the idle instantly arose. Though, I could tell the low was rich cause of a uneven rev and rough idleing. So, I moved the pilot down until the mid range became too lean, I could tlel cause of surging and a over sensative throttle. That is when I moved to the 2nd notch, did wonders for the power. Just a thought.

[kawdude]

I totally agree.  The bottom notch is way to rich and I feel the bike acting as such.   I had the clip in numerous slots just to find out how it effects everything.  What I've noticed is if the clip is in the 2nd position from the top the bike surges badly.  However, it does idle.  My next attempt would be to lower the slowjet.  I believe I'm at a 52, maybe 55.  Either way I drop to the next.  With what you've said above are you implying the mainjet has been dialed in?

[gowen]

Yes, I have power right off the idle, it jumps right into the high rpms, unless I'm on pavement or something. But, if I recall, you are a bit above sea level, so it may not be the same. Who knows.. If you need some jets, I've got them all. Pilot and mains.

[kawdude]

Here's the lastest in the jetting saga...

I spent the day on Sunday screwing with different combinations and it's getting close.  Right now I'm at the 3rd clip from the top, 168 main, and 52 pilot.  

First dropped the pilot from 55 to 52 and moved the clip to the second notch from top  It idled but after running the engine seemed to be constantly "surging" at the idle position...not just when I let off on the gas but as it sat there.  While riding it for several minutes I noted that there was some knocking...piston .  After some key "french" words I started screwing with the air screw.  I cranked in all the way in and the idle cleaned up (surge wise) but wouldn't idle.  Revved the engine a couple of time and turned the screw to 1.5 out, cracked the thottle a couple times and the surges and knocks were back.  Turned the screw in one turn so it's about .5 turns out.  Idle ok, surges ok.  Moral: the surging seems to be a lean condition.  I found that my bike is sensitive to 1/4 turn increments.  Went out and rode it.  Lots of power from 0-50% throttle...big difference in power.  Beyond mid fell on it's face but I'm not dealing with the topend range yet.  By the way the temp was 80.  Hotter=richer...right?

Here's where I'm at...the knocking scared me.  I spent too much cash on this thing to destroy it.  I dropped the clip to the third notch.  No problems at that point but it doesn't launch like it did with the clip in the 2nd clip.  I should have posted this yesterday because I can't remember if the knocking went away totally after setting the airscrew or when the clip was dropped.  I think it did with the screw adjustment but I was still scared that I was too lean and dropped the clip to the 3rd slot.  Am I safe leaving it in the 2nd position?

[KXcam22]

Your jetting saga is interesting reading. Sounds like you big bore guys may be fighting a poor transition between the pilot and needle.  I noticed on a KTM site that  JDJetting.com has made custom Keihin dual-taper needles. The KTM's are notoriously hard to jet and the JDneedle seems to be the solution. I looked and they offer a KX500 kit.  Might be worth a try if it's not too much $$. Anyway have a look. Cam.

[KXcam22]

Sorry guys. Me and my big mouth. I just checked the JD site and they no longer have a KX500 listing, almost no other 2-strokes. Oops. Cam.

[gowen]

Sheesh, that sounds like the problem, maybe I'll shoot them a mail to see if they can still find one left over.

Thanks

[kawdude]

Thoughts on whether or not its safe to leave it in the 2nd notch?  I bet one of the needles JDJetting.com sells would work...

[gowen]

Kawdude, I hit some surging with the 2nd notch this weekend after a few long hard runs on the kx. I was able to mostly adjust the richness/leaness with the air screw.. Which helped alot. It was about 70 degrees outside. So, a bit lean I think. Running a 42 with a 160 main really worked out, it felt a little lean down low and in the mid. Adjusting the air screw did help alot, although it did not completely go away, it worked wonders.

I think maybe the air screw may have did the job. The knocking you are hearing is a spark knock and sounds like you may have been a little lean. I would go back to the 2nd notch and give it a shot. Let me know how it works. I think the air screw should have done the trick..

EDIT:

I'll go into more detail of my excursion from this past Sunday. We have a semi-local place which is 2000 acres of sand. No dunes..   Which has a packed dirt/sand drag strip, which is 3/5th of a mile also has trails that are about 10ft wide and are miles long. Well, anyway, it was seriously a beautiful day, no humidity and 70 degress and not a cloud in sight.  Anyway, perfect day to ride. I came using the 42 pilot, 2nd notch, 160 main, and 2 1/2 turns on the air. Deciding to try a 50/50 mix of pump and C12, just to see if it would work and save some $$$. I started the bike and noticed RIGHT away it was idling funny, mixture of richness and leaness. How do you describe, not a clean REV. It puffed and caughed in a rev. It did not want to cleanly rev through the RPM. Anyway, I would have thought that was rich. Well, as the day progressed, I got to do some 5 mile runs on the trails, mainly 3rd to 4th WOT, preformed fine, still had a revving problem, would not rev through the rpms at a standstill, but would run through the RPM fine in gear.   After about 4 hours of drag racing and racing the trails, I noticed if I hit the throttle it would rev, then surge badly, like keep reving, almost as if the gas was running out.

Anyway, played with the air screw, back to 1.5. Helped ALOT but made it bad in the idle.

That is where I am. :-/ Busted all 3 pipe mounts too.   Serious bummer. Kawdude, if I can get a clean rev without surging in the RPM's at a standstill (Neutral or clutch in) or blubbering, I would be happy.

Overall, the bike performed well, unless I revved it or ran it hard for some time, it did great! I'm going back to  streight C12 to see if that helps.