Just found a very clean, and completely stock, 2009 klx250s (US model). I know enough to know that I got a good deal on a good bike but alas that's where the knowledge ends. I've tried to get a handle on the modding but it just isn't quite clear... So... Here are my riding conditions first - 5000' elevation, slow/tight/hilly technical trail riding, lots of water to go through. If this is true: "Being at altitude and losing 3-3.5% hp for each 1000' of density altitude", then I'll certainly want to get the bike running better. (Is that statement true? ill the KLX actually lose 15%+hp???)


It sounds like the first step in the modding process is to simply "uncork"/"derestrict" it with the end goal simply being to remove the crap that's made the bike EPA legal. I've seen mention of:
1) "shorting the pins on the cable near the clutch"
2) "replacing airbox snorkel with kdx200"
3) replace oem air filter with aftermarket
4) re-jetting, "Is your KLX a hard starter? Drill the enrichment jet to 0.018""
5) "Carb slider hole drilling"
6) "get rid of the crank case breather going to the air box" / "Drilled the crankcase vent hole at the lower front right hand corner of the airbox out to 3/8""
7) "Removed the Air Injection System (Air Valve) that directs clean-side air into the exhaust system right at the front of the cylinder head"
8) "replace the needle (pre-'06 N1TC needle)"
9) extended fuel mixture screw/ kouba fuel screw
10) modify exhaust

Would all of these apply to my situation? What re-jetting would be suggested for my riding style/conditions? How do I get better airflow without compromising the system if the bike gets dunked? Anything/mods I missed that will get the bike to a clean-slate, emissions/mileage/noise be damned, state??

Any help appreciated. Thanks!

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reference threads:

faq https://www.kawasakiforums.com/forum...q-links-30733/

uncorking:
https://www.kawasakiforums.com/forum...-klx250s-2041/

air box/snorkel:
https://www.kawasakiforums.com/forum...3D-safe-40781/

drilling the slide:
https://www.kawasakiforums.com/forum...g-slide-40347/

drilling starter jet:
https://www.kawasakiforums.com/forum...-please-36916/


fixes
T mod:
https://www.kawasakiforums.com/forum...d-water-37960/ [url="https://www.youtube.com/watch?v=cNiI9qCysck"]

disable kickstand switch:
https://www.kawasakiforums.com/forum...-switch-41654/

 

The first mod (clutch cable pins) you mentioned is just for fuel injected bikes I believe

 

I have an 07 and did most of the mods you listed. I also put a KLX300 exhaust to improve the flow. Combined these definitely improved the performance, but it reduced my gas mileage form 63 to 54 mpg. This could be caused the loose nut between the throttle and the seat. The stock carb jetting is actually nearly perfect for 5000 ft elevation but, it too lean for most places (lower elevations). The one mod is not did do was drilling the oil breather path, just could not rationalize it.

 

CaptCapsize, Thanks for the reply. Is the KLX300 exhaust an "uncorking mod" or a performance boosting mod? Put another way, I'm interested in understanding what mods would be done that would achieve a motorcycle that would have come from the factory if the engineers weren't concerned with EPA/mileage/noise standards? My gut tells me if I change those few things, I'll have a bike that runs considerably better than stock. And which mod is "drilling the oil breather path"?

 

Uncorking mods generally involve mods that do enhance engine performance, so it's basically the same term...though uncorking may be more specifically involved with opening up the air intake and the exhaust...more air in, more air out. The exhaust pipe/muffler and intake tract have to meet noise requirements. The OEM carb design and jetting have to meet emission requirements. Fuel mileage doesn't necessarily have to suffer with appropriate mods, and in some cases can improve.

Some of the oldest and most effective mods to most 4-stroke motorcycles involves the exhaust and intake that are then matched with proper jetting. Most aftermarket exhausts are notable improvements over the stock pipe, and letting in more air to match the improved exhaust is logical. However, it all can create more noise both at the exhaust and the intake that some may find unpleasant. After that you go for a better carb and/or more displacement. It's one of the oldest pursuits in motorcycling.

The drilling of the crankcase ventilation path just involves opening up the plastic airbox hole that connects to the rubber hose that connects to the crankcase vent stub off the back of the engine. Not sure how much is accomplished with this, as the KLX seems well designe in handling its existing crankcase pressures. The hole is very small, and it might become more of an issue with a big bore kit. I did mine one time while I had the airbox out doing some other service.

 

If your crossing water, make sure you do the 'T' mod on the carb vent lines.

 

True story...

 

Too funny, but pretty much exactly why you want to do it.

 

Yeah we've got water crossing :-)

 

Thanks for the additional info JaMan. Wow, a friend who rides a KLX dunked his not too long ago and it died... left him scratching his head. I'll have him look into the "T mod".