mod'n this bike was like a crack habit for me....
i started with the 13t sprocket... next thing ya know i was putting on a hiflow snorkel drillin the baffles and rejet'n it (made a BIG diff with just those mods). next thing ya know im droppin over 1k into it in aftermarket pipes and tires (amongst a bunch of other stuff). be careful!!!
[8D]

 

I'm a little different in that I have a dual sported KLX300. I didn'tstart with a 250. Mine is street legal but I mostly ride some serious dirt trails 99.9% of the time. Once in a great while I will cruise around town with no highway driving. The dual sport was only to connect trails if I had to. IMO the biggest bang for your dollar with the KLX will be a 300 bore, a pumper carb,exhaust, and re-gearing. It might sound to low for most of the guys here but if most of your riding is off road 14/50 or 13/50 gearingI find is optimal for the KLX. Stock the 300's come with 14/50 and I find it also works very well around town but would not work at extended freeway speeds. If I'm doing really tight single track I use the 13/50. Also getting the suspension dialed in for your weight is a must do, especially for off road riding. The front end comesset up for around a 140lb rider and the rear for about 170-180lb's
GoodLuck and Have Fun.

 

As several folks have already said, do the cheap / free stuff first, that is: rejet your CVK carb, use YYY.GUY's spreadsheet to see what folks are using at a similar elevation to yourself. In combination with opening the airbox, drilling the stock pipe, and drilling the vacuum slide hole to 6/74ths will net you several HP and greatly improve throttle response. And the price should be less than $30. I'd just remove the airbox lid which will allow you to richen up the jetting a bit for max power.

That should give you a taste of what is to come if you want to keep the bike and continue the upgrades, but just understand that in terms of gains, you are only about 1/4 of the way there, but the rest of them cost some fairly serious $$. So it is at this point that you should probably make your decision as to whether you want to stick with the KLX250S or sell it for something that is already closer to what you want in the end, maybe something like a WR250'ish or something. But how important is being street legal to you?

So if you decide to stick with the KLX250S, and can do your own work, you can get up to what I think is an acceptably high level of performance at a cost of around $1600 to $1800, which is what I've done on my bike:

* 331cc overbore http://www.kustom-kraft.com - $750
* Keihin 35mm FCR pumper carb from Four Stroke Works, http://www.fourstrokeworks.com - $600
* Muzzy full system pipe - $350

You get around 2 or 3 HP from the free mods. The next round above will get you around 6 or 7 HP more. The FCR carb won't give you any more horsepower, but it will take your throttle response to the next level even above what drilling the slide vent hole on your CVK carb did.

If you were nearby I'd let you try mine to see how you like it. I fully understand not wanting to sink that kind of money in not knowing for sure what the outcome is going to be. I recently dyno'd this setup at 27 HP and 20 ft-lbs of torque. Tremor38 says this actually compares pretty well to the Japan-published 40'ish HP due to the way the HP numbers are measured / computed over there. And on a recent episode of Dirt Bike Television, they hopped up a CRF250X with new cams and lots of goodies, then dyno'd it and it looks like the result was right around that - about 25 or 26 HP from the looks of the report though they didn't state the number explicitly, so I think you can be competitive at least in power with your buddies.

http://video.google.com/videoplay?do...83768287949488

But if you really want to get the most out of it, you should also plan on doing some suspension work also. Being a dual sport, the KLX250S is all about compromises. You can address the power by doing the above, but the suspension is also a compromise and would be considered soft by dirt bike standards. You can adjust your stock suspension to compensate a good bit, but respringing to your weight will go a long long way to making it perform better in the dirt.

So the real question is - how much can you afford to spend on your KLX250S vs how much can you get out of it by selling it and then purchasing a new or used WR or similar bike. And if you need to be street legal, don't forget the cost of dual sporting the new dirt ride. I'd be skeptical of you getting $4k out of a used KLX250S. Some people are saying they are buying brand new ones with an out the door price of just a few hundred above that. If I'm a buyer, why should I risk two or three hundred bucks on a used bike that may or may not be in good condition and have no warranty like a new bike does for just a little bit more? Unless you've already got some of the more expensive mods above like new pipe already, I doubt you'll be getting $4k, but who knows you might.

So if you figure a new WR250 will be around $6500 or so. Let's be optimistic and say you get $3500 for your KLX250S. You will need to come up with another $3k to buy a new WR250. If you need to dual sport that, you're going to have to spend a few hundred more at least, so take that into account.

If you stick with the KLX250S, you need to spend about $1800 to get it up to the level of the WR250 or CRF250X. So you are $1200 ahead by sticking with the KLX and modding it. And in the worst case, if you can't adjust the stock KLX250S suspension enough and need to respring it, you should probably figure around $200 or $300 for that, so even then you are around $900 to $1k ahead, and you are still street legal (if that matters to you).

One final point, I went with the FSW setup Keihin 35mm FCR which was $600 shipped. However, several folks have reported good results from the Mikuni TM33 for about 1/2 that much and they send the carb to a fellow who will do a little machining work on it and make it drop right in. So you can save about $300 by going that route. That might allow you to do the hop up mods and the suspension both for the $1800.

If you can't do your own work for some reason, you should figure another $200 or $300 for a mechanic to install a bore kit, depending your your local rates. You don't need a mechanic to install your pipe or carburetor - those are easy.

Good luck.

Here's a photo of mine from a ride yesterday, BTW, with all the mods above - runs great and is loads of fun!

 

Nobrakes I couldn't find a 6/74's drill bit in my index, is that a metric size or something? j/k we all know what you meant. btw I said it somewhere else before but the muzzy looks great with that mx fender.

 

Could that be 7/64ths?

 

Dang it I need to read all of the post before saying anything. I have a habit of reading half of a post then answering. Oh well.

 

Man Deej you need to slow down and get your self a cup of coffee[sm=icon_guiness.gif]. Just in case anybody cares, I did the math and I think nobrakes meant to say that you need a 8/74's drill bit to properly enlarge the slide not a 6/74's which would only be a #46 bit. Wow maybe I need another cup of coffee

 

Sorry for the typo - 7/64th's is the recommended size. I didn't come up with that, I just followed the lead of the smart people who did.

 

wow this post has greatly increased my confidence in the klx, now i need a job

 

Yea Jobs are great!! They allow you to spend money on suff you like.....and other stuff too.