Maintenance & Technical > KX500 Original

Jetting!!! Again and again and again!

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Paul:
Once again, the elusive jetting chart

*** Starting point, not the be all to end all ***

And if you need a refresher on reading plugs

zert:
okay,here is my problem bike.Its a '99 kx5 with a fmf fatty.The bike runs very rich in the lower rpm's,smokes like helldont idle but runs great in the higher revs.When i bought the k5(second hand),its had no power when i pulled the trottle.So i checked the main jet and it was a 182!I changed to a stock one(168) and its was much better.Now i have a 165 and its perfect in high rpm's.The pilot jet was a 55,now a 50 and he still wont idle.As soon a let go of the trottle,the engine dies.The needle is n82l.When a ride on the track or on public roads,the fuel consumption is the same :?.Maybe the previous owner "tuned"the cylinder and screwed it up?The main problem is:how can i make my bike leaner at low trottle?What happens when your reeds are worn?I run almost every week with some other supermotards but i'am the only 2 stroker and now i starting to understand why :-(
So,come on up with the theories and answers.
Regards,
Wim

gowen:
If you are certian about the crank seals, I will tell you that I'm at a 38 pilot. You might have some engine work (like a big bore, porting?). I understand your frustration, I was getting totally frustrated with my KX and getting it right. But, if I were you and Cam might correct me, but in your case I'd try to find an idle. Your pilot jet is your main source for idling.

But before you go on, as Cam said check your slide #. It should have a 6 or 7 stamped on the top. Either way, I found my idle by turning the air screw OUT until it idled, if it wouldn't idle, I'd keep leaning up my pilot until it idled. Once it idled, then I'd fine tune it between the slide and main jet.

Again, I'm down to a 38 Pilot and I get tan crisp plugs and couldn't be more happy with my jetting and it made 100% more power.

Read this article for a better understand of jetting : http://justkdx.dirtrider.net/carbtuning.html

Hopefully we can get you streight. It will be the best modification/tuning you can do to your bike.

KXcam22:
Zert,
  Lets start at the begining. First, the N82L needle is 1 step RICHER than stock. Whoever owned your bike before has deliberately jetted it extra rich.  I can't understand why (yet) unless the previous rider liked to chop the throttle in corners and didn't like the surges the KX will make when jetted nice.  Solution is to not close the throttle in the corners.  The jetting procedure I like to use is to ballpark the main jet (which you have done), get the idle right (as Gowen says) then work the needle, then finish by fine tuning the main.  Sometimes you may have to go back and retune certain areas. Here is what I would suggest:

1. Verify your float level and slide number.
2. Ballpark your main jet (you have done this but expect to go larger)
3. Change the needle back to the stock N82M clip at 2nd to top position.  Given that you are at sea level I doubt you will need one leaner than that, but it is a good first step.
4. Try to get a good idle with only the needle change and your 50 pilot. If the idle still is not right try the next leaner pilot (45?). Some mods make the engine more efficient requiring leaner jetting.
5. With the stock needle and a working idle do a full throttle plug run. For supermoto I am worried that the 165 may be too lean so need to verify it is ok.

Answer back with your results and we will continue. Hope this helps. Cam.

zert:
thanks for the advice,i let you know how it went.(slide is number 7)
wim

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