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Discussion Starter · #1 ·
I have a 2002 KX 125 and it has about 20 hours on it. I do most my riding at about 4500 feet above sea level, average temperature is 80 to 85 degrees F. When I first got it, it ran like crud then I studied a little on the jetting topics and adjusted my jets I found that I had to keep dropping the jet sizes to get a good plug reading now that the plug looks good it has a problem when I go quickly from closed throttle to wide open it completly cuts out as long as I hold the throttle open. HMMMMM! It seems to run quit well except for that. I have also noticed if I go richer on the pilot jet it goes away but I end up with a black plug after a little bit of riding and it almost feels like it is starting to carbon foul(not as responsive). Currently I am running all stock except for #330 main jet, #40 pilot, stock needle on the leanest clip position, I mix my gas at 32:1. It almost seems to me that it is lean but the plug indicates good air/fuel mixture. Thus the confusion sets in. Anyway I was wondering if any one has tips on what the jetting should be at! Thanks,
Dan Dman
 

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Sorry I can't figure out how to transfer the PDF file. But in my "HOW to TUNE my 500" thread, which is like 2 posts down from yours. There is a Team Green PDF file attatchment shifty sent me and the past 3 years are the same. Main jet is wide open problems. partial could be pilot jet and/or clip position. A main jet kit(5-6 jet sizes) is like $20+. The pilots are the expensive buggers. Good luck and run GOOD fuel and premix oil. Makes a big difference.

:)
 

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Discussion Starter · #3 ·
02'KX125 Motor cuts out when throtte is opened quickly

Hey thanks for the info on the teamgreen tech tips, I was not aware that even existed. All though their suggested jetting tips are very close to stock, they are still to rich for my blood. How ever it does make me wonder if I went to a little to lean in one of the circuits. If I went to a 40:1 oil fuel ratio would that only richen the circuits? Again when I got the bike it ran quite rich, I was told by a friend that when bikes are new they actually load them up with grease and oils to protect during break in. Has anybody heard if this is true, and would it make the beast run so rich she spues black splooge out her tail pipe. I have elminated the black tail pipe oils by leaning out the jets. Long story short does anybody know why my motor would cut out when going from closed throttle to wide open really quick. If I open the throttle a little slower it makes the transition all the way to wide open just great. Maybe I am expecting to much, again I don't know!! I just seems like it should take the throttle a little better.
 

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during break in you are supposed to run a different premix and break in the bike a certain way to help everything seat. if your bike dies when cracking it open from idle it sounds like your pilot circuit. What does the plug look like after this happens?
 

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The cardinal rule in adjusting anything from shoe size to head ache pills is to change only one thing at a time and test. Other wise one will never know what worked or didn't work. That said, why not go back to stock jetting, Install a brand new plug, and run a test ride for 3/4 to full throttle in whatever gear is appropriate for the situation. Then stop!! right there with no low speed or idling..pull the plug & read for color. I'm betting it will show a little fat on the main jet at your elev. If so, drop one complete size on the main jet & re-test as before. The accepted practice in re-jetting any bike or quad is to get the main jet right on before messing with the needle jet or pilot. Make certain you needle is in the 3rd position before testing. Not sure what you look for as far a color goes on the plug. If you'd like a photo from a correctly jetted engine you can email me for it. The pic is a plug from a Warrior (4 stroke) but 2 stroke color should be the same. BTW, the 3 jets and their functions are as follows:
pilot--idle to 1/4 throttle
needle jet--1/4 to 3/4 throttle
main jet--3/4 to full throttle
there may be some slight overlap in all, but not much.
 

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Discussion Starter · #6 ·
Am I missing something

I believe my pilot circuit to be fine, when I barely crack the throttle the motor runs great with out spudder. When I got the bike in was rich and I talked to the shop I got it from and they said to JUST drop the needle. So I did once and then twice and I was still fouling plugs. So next I dropped the main jet down one size at a time until a plug chop reading was satisfactory. (Since I have bought this bike I have bought probably 15 spark plugs mostly for plugs chops, I think I should be a pro by now). Then I went to the pilot jet and dropped it down one at a time and adjusting the air screw until it ran good when I cracked the throttle open (no more than 1/8 ) but the only problem I have now is that is cuts out when I hammer on the throttle. It does not die unless I hold the throttle right around 3/4 to full, and some times it catches(fires) at full throttle I will try to start from stock again and move down one thing at a time. Again if I am nice on the throttle it transitions fine through the different throttle positions. Am I just being to picky or does some one think I have a real problem? Anyway thanks for the tips and I will try them and let you know what happens. If any one has any more ideas I am willing to try.
Thanks,
dan_dman
 

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Tuning can be frustrating, I know. Twins are even worse and why I let that one sit. Go back to full factory settings as recommended earlier.
First, Set air screw back to factory recommended setting. Put in fresh plug. Start bike(if already warm then better). DO NOT pull on throttle or ride it. Let it idle for like 3 minutes. Just long enough to get it good and hot. Let idle longer if cylinder is not hot(not warm, but hot). Pull plug and look at the large ring portion. Right where the threads end and flat land is present. Should be pretty free of oil deposits ans buildup. Don't worry about oil in plug threads, always will be there. The flat land should look build up free and shiny. This is primarily the air screw adjustment. If after turning more than 1 full turn out(leaning on a 2-stroke), then drop the pilot jet down 1-2 steps according to how rich idle is.
MAKE SURE to always go back to factory settings(air screw turns/clip position) before changing any jet or clip position.
Pilot jets are like $8-10 @ my dealer and if you are still running factory pipe, I would go right to main jet first. Do, after idle richness setting, a full bore wide open first gear blast up your street(illegal as hell) then close throttle/kill engine and read plug after you push bike back to your house. You won't be that far away since only doing this in 1st gear. Idle then full bore. If ceramic and electrode is all built up it is the main. Then do same for up to 3/4 throttle. If buildup badly enough drop the pilot 1 down then go after the clip position. I chased my tail for awhile on that one. Trick is to not do all sorts of throttle inputs then try and read plug. I bought THE PLUG BLASTER from JC Whitney for $30 to clean up my 12 plugs I used to dial my bike in. Good luck and use 32-1 for break in and 40-1 after about 5 hrs of riding. Nothing less than 93 oct in a 2 stroke for good tunining(I used Sunoco100oct).

Eric
 

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Discussion Starter · #8 ·
Cool sounds like I have a plan now. I have Friday, Saturday, Sunday, and Monday to get this right. Now let me get this straight, I go back to stock and start with pilot jet, now am I trying to get a good plug reading or spudder free throttle response. If I look at the plug after idling I am supposed to look at the outer flat metal just below the threads right? When I get that taken care of go to the main. In response to your main jet plug reading I remember when I was at stock settings at first and I did a full throttle plug reading, I rode hard for about 60 seconds on a straight pass of road and then did a plug chop. The plugs porcelin was all white except for the the lower quarter of the porcelin down inside by the metal, it was black. The threads were black as well. Is this where I am supposed to be looking?
 

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You are correct on idle readings/adjustment. Not far off on full throttle reading. If you ride the bike, using partial throttle to get you to a certain area to open her up, you have already(possibly) pre fouled plug. Man, I have some plugs laying around that have like .5mm(alot ) of carbon buildup on ceramic portion(center) and the actual arch point(hook portion/can't think of word). Light brown ceramic is ideal for wide open. Any "build up" is bad, as you probably know. If you see what looks like bright white spots then it is too lean. Lean is not where you want to be. If compared to a non used plug and not far off on ceramic color, than you are a tiny bit lean(bright white). There are some good spark plug reading sites if you search google for" how to read a spark plug" then, search for 2-stroke. Has pics. of what plug should look like in good tune. Clymer has some old publications of spark plug reading too.
If ridden slowly too long in too high of a gear, you will foul a plug also(bogging it). I have always tuned my bikes(even my twin 2 stroke) by getting idle correct, then rev quickly and dump and hold on til redline in 1st gear only(my 1976 Clymer performance manual states the same). Pull the clutch in, kill it immediately, then push back to garage and read plug. This is for main jet. The pilot and clip/needle position is where you want to do some actual riding time to see about plug readings. So, in a nut shell, the wide open and idle part is easy. When you have partial throttle problems there are many contributing factors. hot_shoe_cv is right on in his post.
 

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Discussion Starter · #10 ·
Ok, I went back to stock settings on the jets and needle. Man that is rich!!So I started with the pilot jet dropping it one size at a time and testing. I found that the smallest pilot #40 jet was the best. I then went to the main jet dropped it one at a time until I found that again the smallest jet #330 for this carb worked best, maybe just a little rich still, but I can not go any smaller because the option is not there or is it? Then I adjusted the air screw until I got nice clean idle and rpms when the throttle is barely cracked open. Now every thing I have learned tells me that 3 and half turns out on the air screw is still to rich, but I am using the smallest pilot jet they offer for this carb. Any way I thought I would put the air screw at factory setting at one and a half turns out and test. Well this cured my cutting out problem but it spudders very bad at this setting and plug has some build up. Does any body know if I can get a #37.5 Pilot and a #320 main jet for a TMX 38 Mikuni carb? According to every thing I have checked on this carb they don't have them. I can't understand why they would not make a jet for this altitude and temp. If I can't get them I may just be screwed. Thanks for all of every ones help, again if any body knows where and if I can get these jets I would be very happy to find out.

Thanks,
Dan
 

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Discussion Starter · #11 ·
Another qusetion, if I pipe and silence my bike does anyone think that would open it up enough that I would not need to go lower on these jets. Or does any body have any suggestions on a way to let a little more air threw the carb. Air filter, reeds, Timing etc......??????????????????
 
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