I have a1988 LT250R Quadracer that has a ported and polished top end, shaved head (that can only run off race gas), a Paul Turner mid range pipe, and a K&N filter with no air box. The stock main jet in the carberator was a #250. I tried various main jets including a 260 & 270. It runs great mid - top end with all three jets. However, it won't idle with any of the jets and it runs bad in the low end of every gear to the point where you have to feather the clutch to prevent from stalling or to get into the powerband. I also tried adjusting the needle jet to the various 5 setting with no avail.

 

Did you try going to a richer pilot?

 

no I didn't. What exactly does that do.

 

My guess is that you're probably running lean on the bottom. Try turning the idle mixture screw out a turn or two more and see if it gets any better. If it does then a pilot jet might be in order, this controls the fuel mixture just above idle but not quite into the needle jet area. Probably to about 1/3 throttle or so.

Make sure that you've got enough jet at the top. Just a couple of jet sizes doesn't sound like enough. On my 86, I went from what I remember was a 220 stock main to a 290 main jet with a FMF pipe, K/N, and no airbox lid. Those were the only changes.

If in doubt start on the rich side and foul a few plugs, it's better than melting a piston!

 

Thanks guys. It was the pilot jet, I went from the stock #30 to a#37.5. It now idles fine, but now the bike sputters at top end with the stock #250 main jet, the #260 jet, and also the #270 jet. It did this before when it wasn't getting enough air into the carb. Do you think I even need to go bigger on the main jet(280 & 290 & 300 are the only sizes left)? Before I changed the pilot jet, it ran like a monster mid - top end, but did not idle and sputtered low end. [img]i/expressions/face-icon-small-confused.gif[/img]

 

the easiest safest way i think to do it is just to go richer and see what happens, if it gets worse then you know to go the other way, check your plugs and experiment a little.

 

It won't ever hurt you to go richer... only foul plugs. Now that you've got a bigger pilot.. that will affect the overall jetting of the bike. You may in fact be rich at the top with stock jets, although I would be a little skeptical of that. Keep going richer and if it gets worse going that way then start going back down until you have a workable solution.

 

Check this site, http://justkdx.dirtrider.net/printcarbtuning.html. It goes into detail about carb tuning.