Maintenance & Technical > KX500 Original
Jetting!!! Again and again and again!
KXcam22:
Gabe,
That Sudco chart is pretty handy. If you really analyse it you can get a good sence of what jets operate where and also where the action of 2 jets overlap. Did you get your needle yet? The sound clips are very cool. Invaluable for diagnosing the surges. My bike has sounded the same. I'll try it tommorow morning (I forgot today) but your sound clips sound very familliar!! At 2-1/2 turns for the best idle it normally would indicate going one more leaner on the pilot, but in this case I think it may be better (since it is very close) to stay with the 38 until the needle is closer. I've never heard of a KX500 with a 38 pilot but it is stock for some CR500's so not unreasonable for the dispacement. I bet that the Eric Gorr porting and all your mods are making the engine run more efficient, hence it doesn't need to be as rich in the mixture. I'll tell you my idea on the surges. If you have ever turned the gas off on your bike and let it idle, when it starts running out of fuel the jetting gets very lean and the idle takes off uncontrollably - and sounds just like the surges. My hunch (humour me I may be waay off base) is that when the throttle is chopped the engine is still trying to pull fuel in (big vacuum) and the last mixture available before the slide actually closed (say 1/4 to 1/8 throttle decreasing) was supplied by the straight section of the needle. You are right about the clip position if the fuel was supplied at the 1/4 and past. A good test for that would be to raise your present needle maybe 2 clip positions and see (heck record!) the difference. If you are going in the right direction the 2-position change should make a obvious improvement to the surges. Will you get a chance to do some testing this weekend? You may have done this already, but it would be worth trying each clip position on that needle to see if any improvements show up (more low end dial-a-wheelie). Let me know the results of your next tests. All the best. Cam
PS. those sound byte are a really good idea!
KXcam22:
Gabe,
Those are good test result (just not what we wanted). Did you try riding it with the CGJ? What slide # is in your carb? So much for my theory.....d**n now I'm really curious. It's dark here or I would go fire up my bike right now. For sure I'll try it early in the morning. Cam.
gowen:
Cam, I did get the needle. I have yet to try a dial-a-wheelie today, but will tomarrow or Sunday. But, the---in the garage---test did show that the surges are still there and have yet to change. I moved back to the CGK and dropped the clip (richened) one notch and it did not change it. But, it did sound better, cleaner. Let me know what you think. The diameter did not seem to fix it, as I kept moving back in the needle CGK,CGH,CGG (or stock), and it still had the same issue. I've fixed the surging by richening the pilot or air screw to the point of rough running and no idleing.
Thanks for the help, I'm going to work on the dial-a-wheelie and get back with serious results, not the garage type. :-) It's getting too dark now.
gowen:
--- Quote from: KXcam22 ---Gabe,
Those are good test result (just not what we wanted). Did you try riding it with the CGJ? What slide # is in your carb? So much for my theory.....d**n now I'm really curious. It's dark here or I would go fire up my bike right now. For sure I'll try it early in the morning. Cam.
--- End quote ---
I appreciate your help! I'm not worried about the needles, as I could always use extras for other bikes or for another rejet or something useful. I sure have not tried to ride it yet, as it is also dark here too. But, will try it tomarrow after work for sure. I will start with the CGK on the 4th clip, then jump to the CGJ at the 3rd, then hit the 4th and get back with you about the exact deal with it.
Also, I'm using a #7 slide.
Thanks again and let me know about your idle, I'm on my toes about it.
KXcam22:
Gabe,
I fired it up this morning and guess what!! My bike surges more than yours does, way more. No less than 6 surges per rev-up and once I counted 12 when it was still a bit cold!!!!! I think it has always done this, perhaps ever since I jetted it way back when - can't remember. This could be a trait of the bike when it's jetted close (maybe). Anyway I guess I never worried about it since it runs perfect all the time. That surging is probably the same as I get when coasting downhill at speed. Again I guess I never worried about it since I rarely coast downhill with the throttle closed. This actually got better when I went from 58 to a 55 pilot a few months ago. Sorry I should have tried my bike sooner and saved you some testing time. The sound bytes are what got me thinking. It might be best to ignore the surges for now and work on getting some more power in the low end throttle range. I still think that new (richer) needle will be the ticket but only your testing will tell for sure. I'm taking the kids out riding tomorrow so I'll be wearing out 1st gear again. Cam.
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