2004 kx 500 not running right. need help!

[cochise427]

I bought this 2004 kx 500 from a privite party. The guy tells me he's did some adjustments to the carb. Because it was running too rich. Really dont know what he's all did and cant locate him to ask. He told me the bike has LESS then 11 hours on it. I can believe him on that one, cause you could put it up to a brand new one and never know the difference. But back to my Questions now that you know alittle about my bike. It seems to me, my bike is running lean at mid to top end as when i let off the thottle my bike still revs alot and chugs bad and pings. Someone told me i might have a bad seal in it sucking air but i thought to myself it's too new for this to happen. So, i'm asking you guys. Could it be? Could anyone tell me all the correct jets sizes that a bike come with, from the factory? i dont know what he's all changed. Right now, my main jet is 168, my slow jet is 55, my needle is n82n i think?... the clip is in the middle and the air jet is turned out 1 and a half out. and i dont know what my slide is. My elevation here is around 2000. and temp is around 70 here. Anyways, if anyone can give me any advise or a starting point i'd be really thankful.

[KXcam22]

Cochise,
  I wouldn't worry.  Your jetting sounds about perfect for your elevation of 2000', the PO did a good job (I'll bet he used the KXRIDERS jetting chart).  I am assuming that this is your first KX500 and that you got it recently.  It sounds to me that what you are describing is the normal action of a properly jetted KX500 when you chop the throttle closed at speed.  We call it "surging" but what happens is that the engine fights for air with the throttle closed and fires erratically as you slow down.  They don't do this with the rich stock jetting and the symptoms only start to show up when your jetting is getting close to optimum.  I run the exact same jetting at 2000' except my needle was all the way down (leaner).  Do a forum search on "surging" and you will learn all about it. My KX was likely the worst offender so I just got used to not chopping the throttle as much when I ride.  Hope this helps. Cam.

Ps congrats on getting the primo low hour KX

[Hillclimb#42]

I helped mine by backing off the idle screw(slide stop). I tend to think it needs to idle higher than really needed. So after backing off idle screw it "surges" less. It still surges, but its only a few extra bangs now. Have to keep that in mind that it does that for jumping the k5. Mine will point you right at the sky with the little burp on the face of a jump that works on other bikes. You really need to be ready with the clutch when letting off to avoid any extra surges at the back wheel at the wrong time. Also, make sure you have just a little slack in the cable and that its snappy on the release. Anything to cut off the air when letting off the throttle will help the surging.
 Pinging happens usually on a top end run, where you have it nailed and the power levels off and you here popping in the exhaust.  That is lean, but I'm not sure thats what you're describing. Use that jetting chart and you have a pipe, FMF and Pro Circuit have jetting recommendations for each year and size bike.
 Also, congrats on the find...

[serafin]

Cochise,  Your jetting sounds close.  I'm at 2000' and 90F  and this is what I run. 165/55 and clip on second notch.  Make sure your float height is set at 16-17mm and adjust your air screw to peak rpm probably closer to 2 turns out.

Serafin