KX 125: couple tuning questions....

[mele63]

2003 KX 125, purchased in stock form, basically new.

First ride, fouled plug, plug always wet when checked. Did some reading here, raised clip one position, went to 35 pilot and 40 main, started out yesterday with a fresh "9" plug, but brought an "8" along with me.

Keep in mind I ride with two twelve year-olds in some pretty thick woods at times, so I understand my bike wasn't designed for this type of use. I thought I was a master tuner until I fouled the "9" at the bottom of a mile-long, basically coasting, tight downhill rocky trail. I put the "8" in and finished the day without a problem.

Questions:

(1) when I checked the plug at the end of the day (not a true chop but after some brisk running), it was clean on one side and black on the other. What does this mean? I'm not sure, but I think the open end of the electrode was the clean side.

(2) If you do a "mixed" type of riding, some tight trails and some open riding, is it possible to "clean" a plug in the open areas? Or, once a plug gets buggered up in the tight stuff, is the "damage" permanent?

(3) I just read here that "pinging" is bad (too lean). Why do the call 2-stokes "pingers? I'm not talking about "knocking" or pre-detonation; just a really crispy sound from the expansion chamber; and finally;

(4) I think I went from wet plugs to a little too white for my liking, how would you suggest getting that nice tan color? Should I switch back to the "9" or keep running the "8" and richen it up with the air screw? I think I'm pretty close on the jets and the needle position.

Thanks.

 

[mczehr]

I have the same bike and I am running the same jetting as you with a 8 plug. Either change your main to adjust to watch ever plug you decide to use or change your fuel mixture. I am running 32: 1. I like the extra oil in a 125. Let us know how it turns out.

 

[Masterphil]

2003 KX 125, purchased in stock form, basically new.

First ride, fouled plug, plug always wet when checked. Did some reading here, raised clip one position, went to 35 pilot and 40 main, started out yesterday with a fresh "9" plug, but brought an "8" along with me.

Keep in mind I ride with two twelve year-olds in some pretty thick woods at times, so I understand my bike wasn't designed for this type of use. I thought I was a master tuner until I fouled the "9" at the bottom of a mile-long, basically coasting, tight downhill rocky trail. I put the "8" in and finished the day without a problem.

Sounds like a 9 is the right choice.

(1) when I checked the plug at the end of the day (not a true chop but after some brisk running), it was clean on one side and black on the other. What does this mean? I'm not sure, but I think the open end of the electrode was the clean side.

Means you probably have the proper heat range. You have to look at the base of the plug for the mixture ring:

Pic shamelessly pirated from Rich.
You need one of these to see down into the plug without cutting the threads off:

Another pic from Rich.

(2) If you do a "mixed" type of riding, some tight trails and some open riding, is it possible to "clean" a plug in the open areas? Or, once a plug gets buggered up in the tight stuff, is the "damage" permanent?

If you are properly jetted, there will be no need to "clean" a plug off. My 125sx will happily idle a whole tank of fuel without fouling the plug.

(3) I just read here that "pinging" is bad (too lean). Why do the call 2-stokes "pingers? I'm not talking about "knocking" or pre-detonation; just a really crispy sound from the expansion chamber; and finally;

Yes, it's that really crisp almost pinging sound that they make.

(4) I think I went from wet plugs to a little too white for my liking, how would you suggest getting that nice tan color? Should I switch back to the "9" or keep running the "8" and richen it up with the air screw? I think I'm pretty close on the jets and the needle position.

http://www.dirtrider.net/gallery/files/1/6/2/4/1/16241-DRN_ca_plugviewer_42.jpg
You want a whitish plug tip. Here is a pic of a plug I pulled from my KTM with very safe jetting:

The insulator(tip) is much more white than the picture leads you to believe.
This is another pic of that same plug:

Coloration on the insulator tip indicates that the plug was not hot enough to burn off the carbon deposits on it. Either because you were running too cold of a plug, or you jetting was so hoplessly off that RC couldn't generate enough combustion chamber heat to burn off all the deposits. Also notice how the black band is much thicker on my plug than it was on the pic of Rich's plug. That's becasue I am running a much safer jetting (more rich) than he was. The jetting on his plug was spot on. Also notice how the pic of my plug has a gray shaded area on the left and right sides of the tip of the insulator. That is not a shadow effect, that is what the plug actually looks like. Probably due to some sort of heat difference because of the intake/exhaust gas scavenging.

You need to take that 8 that you were running and cut off the treaded part and see what it looks like to give you a better idea of your overall jetting picture.

A properly jetted bike should be able to do all of the following:
Have crisp instant throttle responce.
Be able to idle all day and not foul.
Rev cleanly past peak power.
Not bog, cough, or hesitate with even the most ham-fisted riders aboard.

 

[snb73]

mele63,

Here are a few sites to help with jetting. I have a 2003 RM250, I ran all last season on one plug, no fouling. Just follow the jetting proceedures, and you shouldn't have anymore fouling problems.

Good luck, Steve.


http://ericgorr.com/techarticles/carbtuning.html

http://justkdx.dirtrider.net/carbtuning.html

http://www.teamgreennews.ca/techside.html#carbjetting

http://www.teamgreennews.ca/techside.html

 

[mele63]

Thanks, guys.

I guess I need to cut open some plugs to get a true picture of what's going on.