All, just bought my first klx250s about 4 months ago, a new 09. I finally did some upgrades. I put in a 127.5 jet, removed the snorkle and put on a fmf q4 slip on. I also drilled out the air fuel mixture cap and turned it out 2-1/2 turns. My question is...from everything i've read, when you let off, going down a hill or comming to a stop if it is poping it's running too lean...i've read and read so sorry to beat a dead horse. I'm at about 1000'. Should i go with a 130 jet??? Thanks for any help.

 

I think every 4-stroke bike I've ever owned with an aftermarket pipe had a little bit of that decel popping. Not a hunting club full of 12 guage shotgunners discharging their weapons all at once, but some decel popping nonetheless. Unless it's really loud and obnoxious, I don't think I'd worry it.

On that 127.5 main jet, what brand/model is that?

 

Don't jet based on popping on decel. It's normal.

 

jvessels, you just had two of the more experienced members give you as good advice as you're going to get. I'm relatively new on this board, and these two have saved me lots of time by following their advice.

A "burble" is not a problem. POW-POP-POW...could be a problem. That problem could be a leaky exhaust gasket, too, or a malfunctioning reed valve in your air-entrainment smog system. Check the exhaust gasket and correctly delete the air-entrainment system, and report back.

 

I question the 127.5 jet, that's a mikuni jet that's easily mistaken for a keihin in size and shape (threads are slightly different too) but is a lot leaner than a 128 kiehin that you probably want in there.

 

The Dyno jet kit I just installed with mods about the same as yours and with a 128 jet said 3 turns out on the pilot screw, not sure if it will make any change but that is where I started and my FMF pipe pops very little as compared to before the Dyno Jet kit.

 

That's exactly the advice I was looking for! Thanks guys!