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KLX140L DTX/Motard build? (New to PM)

2319 Views 2 Replies 3 Participants Last post by  Luckystar64
looking to rebuild my 140l. It's been used for flat track, enduro, moto, trails, and even pavement. bought the bike new in 2010 and probably has 120 hours on it now. Motor still runs like a top, but I'm dying to make this bike a 20+hp blast. it's going to be a flat track/pavement exclusive bike by the time I'm done (if that day ever comes). I already installed a ballistic battery, FMF powercore, fabbed an under-frame low pipe and hanger for the slip on, jetted/bored the carb to 22mm myself, K&N pod, airbox delete,etc. Had it like this for about a year now, and i'm quite happy. focused on making the bike's CG lower and handling better. now I'm looking for power. at first my plans were a high compression piston for the stock bore and a BBR cam, but nobody makes an aftermarket piston for the 140 in stock size. Engines Only makes a 160cc kit, but plan on spending over $3k to make it run right, plus machining the cylinder, porting the head etc. I hear that there's a much similar bike to the 140L that's a popular seller in Asia. It's called the KLX150S. exact same motor and frame, but just has emission control stuff and lights/signals, etc. I guess there's a following for these bikes over there, and people mod them into stunt bikes/Honda 150R killers on supermoto tracks. Kawahara makes a 63mm (180cc) piston kit that comes with everything down to the rings, OE bored cylinder and gaskets. Equating the exchange rate, the whole thing can be had for under $500 with a forged 11.5:1 piston! A matching OEM big valve head and copper seats, already matched and ported, runs for around $300. Add a Web racing cam, and you'll have a killer race motor for under $1000. Did some research on the kits and people who use them overseas say they last for about 80-100 hours on 93 octane. not bad. Faster guys claim 50. I have a 28mm carb off an old XR100 race bike, and I've machined an intake to fit on CNC and Lathe. A local guy says he could lighten the stock flywheel for cheap (He's an XR100 guru, and has done the same to a 140 he owns and races). I'm pretty sure the stock suspension will suck after the build, as it can barely keep me (5'8", 190lb) and 10 horsepower in check, but the back shock seems to work way better than the front forks. Any of your suggestions would be great. Thanks.
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This thread belongs in the "bigger minis" sub forum.
It seems like you have done your homework and you should have a fun bike when it's done. I would look in to switching over to a different shock, I believe that kx85 shocks fit, but I may be wrong. I'm sure you can also replace the stock fork springs with stiffer ones and use thicker fork oil. Look in to modifying the dampening rods, I know it is popular an the kx65 forks. Race tech also makes a form emulator which allows you to adjust the front forks, but I'm not sure if they make them for your bike. It's supposed to stiffen up the first few inches of travel pretty well.

I would also double check and see how the reliability of the big bore motors is. There may be a few supporting mods you don't want to leave out
Sounds like a cool build. I worked with a 140 when it first came out, and I'd love to work with one again. I've been on 150F's though, because the motor is easier to work with, the suspension is better out out of the box, and it's kickstart. I'll keep an eye on your project. I have some ideas on suspension. Let me know if you want my input. --L*64
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