confused jetting

[Polar-Bus]

try next size hotter...7

You should NOT band-aid a ill running KX500 with a "hotter" #7 plug.  Get to the true root cause and correct.

[Polar-Bus]

im really confused on my jetting situation,heres the deal 2003 kx 500 all stock even the brass, compression good with fresh top end, reeds, etc. mix fuel 93 octane klotz 32:1, elevation 2000ft, air temp 60deg. stock jetting is real rich so i droped main jet to a 165, pilot a 55, and needle clip to #2, air screw 2 turns out. bike ran cleaner but still had some studdering at 1/8 to 1/4 throttle, looked at porcilian of plug at base, had black ring half way up then rest was dark brown, so i leaned it out more. main 162, pilot 52, needle same clip #2 and airscrew 1.5 now my plug is still black half way up porcilian but rest way up is off white, from every thing i read there should be a brown ring a few millimeters up from base no black, my question is should i go to a 160 main? but every jetting chart i see from pro circuit to team greens all are at or close to stock jetting. i want max power but in order to get my plug to read right i need to lean it out beyound my comfort zone. should i go by the base of plug color or keep jetting to rich with what i got.

OK, i'm going to ask the question again that I always ask when someone describes your engine symptoms... what exactly is "good compression"  is this just a guess or have you done a real compression test with a guage ?

[bige]

compression is at 150 tested with a guage. i can deal with the surging somewhat just trying to get used to it but i want to get that 1/4 throttle response cleared up and stop running choppy and studdery but im afraid of going leaner than a 55 on pilot jet, with that jet i get the fastest idle at 1.5 turns out on air screw. jetting this bike is a real pain thats why ive been studying on plug color and how to read one correctly thats where the mixing ring is supposed to be at the base of porcilian and brown not black but if i go by that then i would be at a 160main,52pilot with needle in the #2 clip posisition and air screw 1.5-2.0 that is crazy lean to me. but someone said that it doesnt matter if the whole porcilian is white as long as there is a 2 millimeter brown mix ring at the base. has any body jetted their bike this way?

[Polar-Bus]

compression is at 150 tested with a guage. i can deal with the surging somewhat just trying to get used to it but i want to get that 1/4 throttle response cleared up and stop running choppy and studdery but im afraid of going leaner than a 55 on pilot jet, with that jet i get the fastest idle at 1.5 turns out on air screw. jetting this bike is a real pain thats why ive been studying on plug color and how to read one correctly thats where the mixing ring is supposed to be at the base of porcilian and brown not black but if i go by that then i would be at a 160main,52pilot with needle in the #2 clip posisition and air screw 1.5-2.0 that is crazy lean to me. but someone said that it doesnt matter if the whole porcilian is white as long as there is a 2 millimeter brown mix ring at the base. has any body jetted their bike this way? 

OK, so compression is good so you don't have a weak top end. In your first post you commented that stock jetting was "too rich". My question is what are you basing your claim of "too rich" on ? You are claiming your engine has lean surges at 1/4 throttle correct ? This is a tell tale sign you are too lean, not rich like you are claiming. Problem i'm reading is that you are just throwing multiple jet combinations all at once  at your engine without any single carb circut systematic method. For example you are first supposed to do a WOT plug chop to get your correct main jet. Then you work the pilot jet, and if needed adjust your needle clip position. If you are getting lean surging at 1/4 throttle that is most likely your pilot jet. Keep in mind if you have an air leak, attempting jetting is a waste of time.

 I run a 165 main, 55 pilot and clip #3 position with great results in temps around 50-70F

[Letsride614]

I have a gnarly pipe and powercore silencer and FMF recommended 165, 52, and clip in 3rd. I had to go to the 2nd clip to get mine to run right. I run harescrambles with lots of single track and it will still load up but cleans out and burns fine on the fire lanes. It could probably go to a 50 and be ok. The FMF jetting is for desert or mx according to them at sea level so its just a baseline and will vary depending where and what you are doing with it. Good luck as it can take some time to get it sorted out.

[bige]

the surging is only with CLOSED throttle going down hills it lerches back and forth. it runs fine upon throttle only at 1/4 throttle does it studder just like its to rich there. from 1/2 to full runs clean.

[bige]

checked the piston for wash and there was none which tells me im way to lean, im going back to stock jetting ride it a while and check the wash heck might need to go richer on the main. seems like piston wash is a better indicator than plug reading