Maintenance & Technical > KX500 Original

Jetting!!! Again and again and again!

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Glenn_KX500:
Why would I have to compensate with the needle position?
Isn't the surging due to the pilot circuit being lean?
What do you mean by sacrificing the idle, do I have to go so rich to get rid of the problem that the bike won't even idle afterwards?

gowen:

--- Quote from: Glenn_KX500 ---Why would I have to compensate with the needle position?
Isn't the surging due to the pilot circuit being lean?
What do you mean by sacrificing the idle, do I have to go so rich to get rid of the problem that the bike won't even idle afterwards?
--- End quote ---



Glenn, I'm with you, I would have thought that the surging is due to a lean pilot. But, in this case, I'm assuming vacuum due to the mass of the piston. This really sounds stupid, but I've tried everything! I can get an idle with no surging, but end up having to get a longer idle screw. To completely eliminate the surging, it seems that richening the pilot mixture does not completely help, but bringing the needle a step richer does. They work together in this regard. But, you might have better luck, I was doing testing on the east coast at sea level and about 80-100 degrees. Now we are down to the 60s, but still crisp jetting and a little lean at times, but can always compensate with the air screw or needle clip.

A few of us folks that have chipped information about Jetting have all decided that the surging is a GOOD sign and means your jetting is just about right on.

Also, with the pilot rich and needle rich it effects about 20% of the power due to incorrect mixtures of the fuel/air. With that in mind, it's all up to preference, 20% is a huge amount, but the big KX already makes too much power, so most people don't care  :wink:. But, I like to squeeze every ounce of power out of my bikes and the biggest improvement in power is the jetting.

KXcam22:
Hi Glen,
  Welcome to the jetting forum. Yes the surging is a bit of an enigma.  When your jettings lousy there is no surge, but as soon as you start getting close the surging appears.  I know it shouldn't surge but I'm not sure what the fuss is about (ok I know it's annoying but I just got used to it to the point that I forgot it does it - ask Gowen).  Mine is probably the worse offender I have come across but it doesn't bother me at all when riding. I suppose if you normally coast through corners it might be an issue, but its way more fun and the big KX loves a handful of throttle in the corner with a big wheelie out of it.  I do notice it coasting down mountain roads but then I don't care.  I know it's not much of an answer.  If you are willing to do some testing I would be happy to lend any advice I can. Two things I would like to test are intake volume changes and different carb types. Both tough to do. Cam

kawdude:
Thanks for all the good information.  I think I finally tuned it in.

gowen:
I have to say, the KX is a bitch to tune, but once tuned... wow!

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