I'm curious when you perform the big bore 300cc, is the power the exact same as the KLX 300? Or is the KLX 300 still different and more powerful? Just curious.

 

I think it makes them pretty much equivalent. They both have the same carb, cams, etc, etc. Even if there are some minor differences here and there, I doubt its going to add up to a lot of performance differences. The KLX250S is basically detuned for street legality, while the KLX300 is off-road only so it is set up better in its stock form. But once you rejet the KLX250S, open up the airbox and exhaust, it's a completely different bike. Add the 300 kit and there's really very little difference if any.

And I will say that adding the 300cc kit added quite a bit of punch to the 250, all across the RPM range. It's 20% more displacement afterall. It felt like the increase I got from the jets, airbox, and pipe mods all over again.

I've got a Keihin FCR 35mm pumper on order. We'll see if that notches up yet another level.

 

The CDI on the 300 and the 250 is different. The 300 CDI is tuned for more aggressive/responsive/off-road riding. If you want your 250 to truly run like a 300 then in addition to the big bore kit you ought to switch out your 250 CDI for the 300 CDI. Unfortunately, this requires some re-wiring :-(

The KLX 250 has been on the market in Japan for over 10 years now, and the CDI mod is one of the first mods that guys do over here (I live in Japan). There are wiring diagrams posted on the Japanese web showing how to hook the CDI up. Here's a link to one. Instead of the 300 CDI, this guy used the 250SR CDI which has the same timing as the 300.

http://www.dfreak.com/ign.htm

By the way NoBrakes, I'm interested to hear how your FCR fits up in your bike. I've seen FCR's installed on KLX 250's over here and there's always an interferance issue with the head pipe. Most guys either hammer a dent in their head pipe or wind up mounting their FCR's at an angle (10 to 15 degress off vertical).

 

Thanks for the info on the CDI. I'm just having a little difficulty reading this wiring diagram.

 

I will be sure and fill you in when I get it and get it installed. I paid somewhat extra to get it from Four Stroke Works, http://www.fourstrokeworks.com . I called them up and FSW is run by Jerry Lieghton who is now retired working out of his home. Jerry is formerly of Stroker, the KLX experts with the rather famous Larry Roeseler. I spoke with Jerry for a good while on the phone and he really knows his stuff and knew all about the KLX250S, its similarity to the KLX300, and the specifics required to fit the Keihin FCR, Mikuni TM, etc. He seemed to know exactly the fitting issues on the KLX250S and specifically mentioned issues with it clearing the starter motor. He said he sets up the carb and boots so it is ready to drop in without any fitting issues, having already worked that out. I got the impression that he uses a different set of boots between either the carb and airbox, carb and engine intake, or both. Another advantage of buying from him is that he sets up the jetting and other carb settings to a good starting point. From what I understand the FCRs have more adjustable settings than our CV carbs and can be a little finicky to set up for a non-expert. But once tuned, they really scream. He also takes the time to learn about what you want out of it and makes recommendations that are reasonable to get you where you want to be. To me, that level of service and drawing from his many years of expertise is well worth more than his mark-up on the carb itself.

I'll let you know how it all works out.

Oh, and ditto Finger Mullet on the CDI diagram - you don't happen to have a translation for that do you? An upgraded CDI could potentially made another good performance gain. I seem to recall there is even a wiring adapter you can get from somewhere that does these pin cross-overs for you without having to cut into your stock wiring connectors. Anyone have a link to that?

 

That is some funny crap!!![sm=roll.gif]

 

NoBrakes, thanks for the detailed report on your conversation with Jerry at FSW. I spoke with him on the phone too when I purchased my FSW header and muffler last year. He does know his stuff. And his stuff is expensive!!!

Below is a link to a Japanese racing company that makes the wiring coupler for popping in a new CDI. I've already purchased the CDI (about $250 USD). But I don't want to pay the $150 that K&T charges for the lame little wire coupler to install it. I'd rather make my own (should be a piece of cake), but I can't figure out where to buy the dog-gone little wire connectors that I need to connect to the harness on my bike and to the new CDI. Anybody know where I can get these kind of connectors on the web? They ought to cost just pennies each (I think).

Once I get this figured out I'll do a write-up and post it here...

Here's the link:
http://www.kt-bike.co.jp/dt/180610.htm

 

Regarding his prices, yes there is definitely a mark-up there, but it doesn't seem too horrible to me, at least for the carb. While I can't seem to find a price specifically for a Keihin FCR 35mm carb, I think you will pay around $500 or more, but lets say $500. That typically doesn't include jets, etc, but those aren't too expensive. You still have to deal with fitting the carb, getting a good initial adjustment and the like, which can be difficult and time consuming if you haven't done it before. Jerry sets it all up for you ready to drop in and sets up initial jetting and supplies extra jets for adjustments and also tuning tips. He charges $600 for the whole package. For my own situation, I'll gladly pay the $100 extra for his knowledge and for me to not have to do all that myself. But I guess it depends on your expertise - no sense paying for his knowledge if you have plenty of your own.

But the price on that adapter - man that is highway robbery. I wouldn't think that would be more than $15. I'll be on the edge of my seat if you translate that diagram and get it wired. I'll even buy a connector from you if you are so inclined to make up a few. But not for $150

 

try auto electricians, hobby shops, maybe car audio shops