I just did a craigs list trade yesterday and part of it was a 2009 klx250s...
I am a car guy: just sold a 12 sec evo 9, Used to own a Ducati 916 and tracked it regularly, have a 4bt powered toyota on one tons...
So Im not mechanically helpless, but Im not very experienced with carbs and dirtbikes. ive rebuilt a few honda lawn mower carbs but thats about it...
The problem:
Yesterday and this morning the bike seemed to run good. It seemed to have a slight random miss when going down the freeway at a steady 70mph, but besides that it ran pretty good. It had a dead spot in the throttle at low RPMS, but I figured it needed a plug and mabye a jet kit from what Ive read...
This afternoon I changed the plug with an identicle NGK, gapped to .30, and changed the oil because it was scarry dark. I also pulled the top of the airbox off and cleaned the aftermarket filter. After all this it starts up way better and idles great, but then I went to ride it. It misses and hesitates badly over 4k rpms. If you give it more throttle than 1/4 or so it just kinda boggs or misses. Pulled the plug and it looked white to me. Lean is what it felt like, it doesn't feel like its bogging from too much fuel. Def not enough.
Its full of gas. I played with the res/off/on fuel valve. I drained the carb bowl to make sure it wasn't water or crud.
No change.
What did I do to make it stop getting fuel? i even tried cracking the gas cap incase it was vacume locked.
Thanks for the help!! Im just starting to read and appreciate these forums.

 

Carb may be gunked up from storage by the previous owner. Run some injector cleaner through it.
You may want to do the grounding mod, as that started that year I believe. There is another thread on it and it is easy to do. That causes a missfire about 6Krpm.
If you left the top of the air box off, put it back on, that will really lean out the bike and cause your symtoms.

 

ok I'll try that. I thought more air was better. Do I need a jet kit before I can open the airbox up?
Thanks.

 

Yes.

Everything durielk said is what I was thinking too at this point. And the ground he was talking about is the rectifier. You can search it.

 

Post some pics of the Yota on tons. I've got a K5 crawler on tons.

 

You guys were right. I should have realized that was the only thing I really changed. Didn't think it through. Surprised they come that restricted from the factory. This bike has a two brothers pipe and header on it so I guess that mixed with the air box just leans it out way too much. Time for a jet kit. its still cutting out from 6-7k RPMS at steady throttle. I'll look up the rectifier ground mod. Thanks.

 

Nice Blazer! its an 84 yota and the cab is currently off... Im in the process of linking it and finishing the 4bt swap. Saving for an atlas... got a 47RE. it never ends.

 

Sounds like it will be nice. But yes they are never ending money pits.

 

here is the rec mod