How to use the 125/250 36mm/38mm carb.

[factoryX]

1. Buy a rad valve for the KDX
2. Take the rubber connector and flip it around(Tight fit!)
3. Done. Larger carb now fits

If everything lines up okay, you should be able to now use the stock 125/250 air boot/box.

[doctord23]

I have tried a couple different KX125 carbs combos on my Hybrids with the following results:
1. Mikuni TMX38 from a 2002 on the 220 engine with a desert pipe and RB head = amazing low end and less top end than a Keihin PWK. This seems counter intuitive since it is a larger diameter carb than the KDX 200 carb.
2. Keihin PWK36 Powerjet carb from a 200 KX125 on the 200 engine with desert pipe = runs strong and I am still running it. The powerjet has no connection and the TPS had to be removed in order to clear the frame.

The TMX carb is very thin and fit well but the overall power (except low end) is not close to what I get with a KDX PWK35 air striker.
The PWK36 is a tight fit due to the extra components (which are not used)

My experience. Your results may vary.

[factoryX]

I am running an earlier pwk 36mm of an 98 kx125, has the twist cap and no tps. Was awesome how much over rev I gained from the swap along with the rad valve, and still retained low end.
Ran a 38mm pj carb, was not impressed with it.

[Tyl3r]

2. Keihin PWK36 Powerjet carb from a 200 KX125 on the 200 engine with desert pipe = runs strong and I am still running it. The powerjet has no connection and the TPS had to be removed in order to clear the frame.

What year KX125 are you referring to here? After reading this, I am wondering if I can use the stock Mikuni TMX38x carb off of my 2005 KX125 for my 220 hybrid? Would sure make airbox/boot fitment a lot simpler. If I could get bottom end benefits from the swap, all the better lol What is the jetting like compared to the stock KDX carb? About the same?

[factoryX]

With this set up, as long as the stock intake lines up with kx125 airbox boot will work.

[Tyl3r]

My main concern is with jetting/performance rather than fitment. In building the hybrid, I'm putting a new top end in, freshening up some things, and throwing in a V-Force 3 block. Right now, I am confident that the jetting is good for the stock reeds, a Gnarly pipe, and Powercore II silencer (same exahust set-up that is going back on it). I feel I could start the bike up with the stock carb and current jetting and it will run/idle just fine.

I worry if I swap carbs too, that the bike is going to run like crap for the break in period, and then I'm going to have to fiddle with it to get it to run right. So basically what I am wondering is what was the jetting like on the stock carb, compared to the jetting the TMX38x? Big changes? About the same? I know that it is larger, so more air is moving in there... so I'd want to dump a little more fuel in there, correct? Just would like to get it in the ball park before putting it on.

P.S. I think its awesome that you guys have found this out and can share your experiences, thanks for sharing!

[factoryX]

I'd just break it in, and if you want to try a larger carb, then go try it. As for jetting, I doubt it will be close. I ran a 36mm carb on my 03 yz250, and I am now 5 sizes higher with the kdx.

[factoryX]

Hey doctor, what jetting you running on that 36?