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KLX250S stumbles at 62mph


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I haven't pulled the plug yet to see what it looks like. I just got home from riding all day and I need a break for a minute. Here's what I got. I got a 2009 KLX250S with a Uni air filter, snorkel removed, dynajet kit stage 2 set up exactly as the instructions said, and a FMF Q4 pipe and the header is stock. I'm at 700 feet of elevation. Also the front sprocket is 13 tooth. So at about 7,000 rpm I'm going about 62mph. When the bike is colder, like in the first 20 minutes of the ride(it's 48 degrees out) it's fine. But after a while I'll be cruising down the highway and I'll feel it stumble and miss a little if I hold it there for any length of time. It's only around that speed that happens. Anyone else have this? I'm thinking it's just a little bit too fat and maybe I should do a plug reading and maybe end up dropping the needle one notch. I got the needle set in the middle and the pilot screw is out 3 turns like the instructions said to do. What do you guys think?

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Try shoving the stock snorkel back in the box, see if it gets better or worse. Then again with the box lid off.

I just experienced the same thing when I put a K&N filter in. For now I have just lifted the needle and put the box lid back on with a kdx snorkle, but it may need a bigger main also. I suspected the klx300 needle taper but since your having the same issue with a DJ it may need more main jet.

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I have an 09 with the same issues as well. For me, it's intermittent. Both on acceleration and WOT. But always at 6000 to 8000 rpm. My set up is basically the same as yours. Yesterday, I changed from a 128 DJ main jet to a Keihin 130 main. My DJ kit did not have a 130 mj. My problem is mostly gone. I'll try raising the needle to get it perfect. The DJ 132 main jet was too large. Ran really rich.

Here's the rub. Maybe I'm crazy but before I changed the main jet, I went through all the ignition system checks in the service manual. Everything checked out OK. When I rode yesterday, the stumbling only occurred once briefly right after I hit the rev limiter. Don't know if unplugging the cdi during the checks had anything to do with it? Further experiments required.

In other words, I don't know for sure what caused the drastic improvement with the stumbling problem. The main jet swap or the cdi being unplugged for a while.

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