Air Box Lid and Jetting

[kxjet]

New to carb tuning

:yikes: I took my carb off last night, and the intimidation factor set in. So lets see if I got this right. The Air Screw will change my off idle throttle response? Can anyone tell me what the "tell" signs are that would indicate a rich or lean condition? I just read the carb tuning article at JustKDX and was hoping to get a little more info.

 

[John Harris]

Fellows, every bike is different. But, I have found by trial and error on my relatively stock 200 bike that you can help by going lean, lean on the primary and then if you err, err on the rich side on the main you will have good performance and engine safety also. On my 200, I have enjoyed the 40 primary and 155 main combination. I could not imagine using a 40 primary until I tried it and found out how much it helped the transition to the main because (I think) it did not have to clean out the rich from running on the too rich primary. And you do have to adjust your air screw to match the temp, humidity and primary. Ride on --John

 

[kxjet]

I'm just a little scared to take it lean. About a year and a half ago I trashed my old 125 in Colorado. I had to lean it out to get it to run right, but it only took a day of riding and the piston and jug were screwed. After reading all of these posts it looks like a 155/45 setup would be a good starting point. I'm just nervous cause I love my KDX and want to keep it FOREVER. It doesn't help that I really dont know what I'm doing when it comes to carbs, and when I read some of these threads it's like reading greek.

 

[Roland C]

kxjet: KDX's come from the factory jetted rich (160 main and 48 pilot, I think). Buy some cheap standard "s" NGK spark plugs (B8ES or BR8ES) and do some plug chops. The info you got off of Canadian Dave's JustKDX site tells you how to do the plug chop. Start with the 160 main. Then do one with a 158 main. If you still look good (which you should), drop to a 155 and do another plug chop. You definitely want to get the main jet dialed in first. Playing with the pilot, air screw, and needle won't really get you where you want to be if your main is off. When checking the plug, it is best to remove the threads (probably with a vise and a hack saw) so you can see the mixture ring at the base of the ceramic. When the main is on, the mixture ring should be about 1-2mm in thickness. Don't worry too much about how dark it is, concentrate on how thick it is. If you've only run a brand new plug for 30 seconds or so to get a plug reading, the mixture ring won't be very dark. Once your main is good, then start playing with the other circuits. The big thing is just doing it. Once you start to play with it and get a feel for it, the intimidation factor will mostly go away. Even though all KDX's are a little different, I've never heard of anyone seizing with a 155 main/45 pilot. Good luck and let us know how you come out.