I have an '09 KLX250S with the Kustom Kraft 330cc kit installed. Having a little trouble getting the stock 250 carb jetted. If the main jet is good it surges at cruise rpm. If lifting the DynoJet needle to stop the surging and going up a little on the main jet it is too rich at wide open throttle.

Anyone used the KLX300 carb with the different needle jet and needle on a 330cc motor? Does it work out better?

 

That's interesting. As clearly evidenced by many here on the forum, the 250 carb should work fine if jetted properly on any big bore kit. The 300 and 250 carb are basically the same and respond similarly to jetting.

 

I would like to see some of the jetting people ended up with if they will chime in. I'm not a novice on jetting but this one has been more difficult than most to jet.

I'm running a KLX300 header and muffler with the tip in place and a K&N filter, KDX200 snorkel.

I remember seeing a couple of pages of jetting records but can't seem to find it now..... That might give me an idea of the next move if someone can point me to it. It was actually for the 250 motor I think but might be of help.

 

Have you upgraded the clutch? Stock clutch couldnt handle the factory 292cc kit.

 

I'd try getting rid of the snorkel. You could be starving for air.
Also playing with tape on the lid can be easier than jetting to see which way to go.
good luck
marc

 

aprox what mph, gear, rpm and throttle position are you noticing the surge?

did you try the needle lifted and going down on the main?
if the throttle position is just cracked you might try the fuel screw, moving the needle still has you on root diameter and doesn't change

might also try it with a foam filter

also is the bike good and hot when testing.

 

What's your elevation and which jets are you using as all aren't created equal. Also a lot of guys with stage 2 jetting didn't need to change much at all for the big bore so that is a starting place.

 

Bike is good and hot. Surging is at around 7,000 rpm, cruise throttle, about 5/8 to 3/4 open. 15 39 gearing for highway. Riding at 8,000' to 9,000'. Temps around 65 to 70 degrees most of the time.

Dynojet Stage 2 jetting way too rich at this altitude at full throttle, but lean surge still occurs.

I think I'm getting close now with Keihin main 120 and DynoJet needle in 5th notch. Surprised it has to be set that high but that may be the fix for the surging. Haven't tried it that high before. Idle mix screw out 2 turns. Haven't been able to ride and test since raising the needle to 5th notch. K&N air filter and KDX200 snorkel. Lean surge goes away if running with enricher pulled out with all other jetting tries.

Looks like the needle will have to be in notch 5 as I now have it. Should get a test ride in today.

Pulls hardest wide open throttle with the 120 main.

 

The way you explain the surge it could be a problem seen on some of these bikes from a poorly grounded regulator there is a thread on it somewhere, as the folks that have had the issue notice it as you describe. The enricher wouldn't affect it if it was electrical but I still wouldn't rule it out as if this is your issue I'd go with the 120 jet and add the ground and see what it's like.

 

I'm familiar with the regulator ground problem, planned to do it to prevent any future problems in that circuit but haven't done it yet. The enricher pulled out definitely kills the surge so it doesn't look like the regulator right now but I'll do that mod soon, it might be giving a misfire on the leaner cruise mixture rather than the full throttle rich mix. I'll post results. I didn't get to ride yesterday as I had planned, maybe today.