I know this is of topic and not a dirt bike forum, but I figured someone on here might know. OK, heres the deal. One of my riding buddies bought a used "95 YZ125. It is all stock except for a Pro Circuit Platnum series exhaust. The problem is that the jetting is way off. It runs too rich and keeps fouling out plugs. It also doesnt seem to want to really hit the powerband that well. He can't really seen to get it to wheelie that well. One of my other riding buddies picked up a new '03 YZ125 and that thing will wheelie like nobody's business. Anyone have an idea at what the jetting should be and what the setting on the carb should be? Thanks for any help.

 

95 vs 03 ok I think Yamaha has made quite a few changes since then.
But about your ? First before you go into the carb better check compression. If a 125 dont start on the first few kicks its time to redo the top end. both of your comments would lead me to check that first especially if its used who knows whats in there.

 

It starts within the first few kicks. We thought it might need a top end rebuild, but we checked the compression and it is good. We know that it is in the carb. If you let it idle for more than afew minutes it will foul a plug. Im talking he would go through 10 sparkplugs in one weekend. That tells me it is something in the jetting. And the plug is black, real black

 

Check for a cracked reed as well, my buddy had a simualr problem and it was a cracked reed.

 

Good, thinking, I will have him check that too.

 

I had a '02 CR125, brand new, and completely stock, and the thing would CONSTANTLY foul plugs... Pain the butt. You could NOT idle it, you had to constantly rev the engine to blow the oil out.

I talked to quite a few bike mechanics, and they all said basically the same thing... "125's are meant to rev, not lug. They need the rich mixture to keep from burning themselves up." So between that, and the un-holy noise that the pipe emitted (I couldn't even hear myself think), I decided that I was a four stroke man, and sold the damn thing for a Warrior...Which will be the wifes once I get the dough for either a Rappy or a 450... Or a Honda wheeler if they ever get off their butts and start competing!! [img]i/expressions/face-icon-small-wink.gif[/img]

I don't know if you are going to do any dunes, but it had NO low end power, and was a joke in the sand, I really worked that clutch hard...It did however, have nuts on the top end, which made wheelies easy and fun. I would definately recommend dropping a tooth in the front, and going with short paddles (no more than an inch tall). I had a Cheng-Shin paddle tire, and they were WAYYY too tall...if I recall, the paddles were about 1.25" to 1.5" tall...Also go with a smaller tire than stock, or the paddles will rub/HIT the swing arm.