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Does the KDX take a special OEM style throttle/cap that angles out for the tank? I remember something about that. The extra 10mm will surely help. Simply boring your carb to a 36 will net some of this without the swap.

yup it's at an angle

Well, moto psycho, I know a lot of people are kinda beating you up about this, but I like your attitude; you're right, modifying **** IS fun, this IS a hobby, and who knows, even if the larger carb doesn't work that great, it may well lead to an idea that DOES work great.

I've been involved in motorsports of various kinds for 35 years (holy crap, I just realized I'm OLD, ha!) and I've always learned just as much or more from my "great ideas" that didn't work, as those that did. One of the greatest engineer/race drivers ever, Mark Donahue, once said that he reckoned only 20% of his "great ideas" worked. That's only 1 out of every 5! The 4 out of 5 that didn't work inspired the kind of car development that made him a legend. So carry on!!

Thanks for the link about water injection into the pipe. I would NEVER have thought of that, and the idea is interesting to say the least!

Valid point. However, it's been shown not just in motorsports, but in every application for an IC engine, that a carb which is larger than needed is ALWAYS detrimental to performance. It's not like this is breaking new ground.

scheckaet wrote:yup it's at an angle

Oh no :( i'll have to bend the new one

Mine is an SR, steel tank, loads of room underneath.

juliend wrote:Valid point. However, it's been shown not just in motorsports, but in every application for an IC engine, that a carb which is larger than needed is ALWAYS detrimental to performance. It's not like this is breaking new ground.

And please show me the calculations that prove that a 36mm PWK is better than a shorter 39mm PWM? People seem to have tried the PWK38, but not a PWM39, whole different kettle of plankton.

Let me ask you this...

What exactly is it you are hoping for from your KDX? Are you trying to set it up to race? Riding trails? what?

The PWM does look nice. It's still a 38mm carb, and will flow considerably more air than the 35, much less the 28mm that your bike was originally ported for (you do have an SR, right?). This is a big change!

Like Fuzzy said, I'm sure it will run. If you can get it jetted right, i'd expect a dramatic decrease in low end power, and some more power up top. Unfortunately the KDX doesn't rev out far enough to take full advantage of this. I doubt your "cleaning up" of ports will do much to improve this, but who knows?

I don't suppose there will be any data in regards to the 38mm PWM on a KDX. So I'll give you that much.

I'll stop arguing with you now, and sit back and wait for your results! I'm interested to see the fitment for sure, and how you progress with a divider plate.

I simply wouldn't expect the power shift to be dramatic enough to warrant the labor is all....One way or the other. I'll bet she still pulls pretty well down low. My 250 with a 38 is a tractor, but not as good as with the 36, but is a different animal. The netted gains on the top end (as mentioned) would be minimal without some serious port and head work....again hard to justify. Did you just spend a ton of time getting a 35mm PWK working? THAT over the SR 28mm is a great thing.

I know of a few of the last air cooled KDX200's that have been hacked on for karting running Mikuni Super-BN 38-40mm pumper butterfly carbs, BUT they are beasts. Heads and ports wildly hacked and along with the carb setup for methanol. magnetos installed. Custom pipes. Custom built intakes/reed cages. Transmissions cut off. 14k RPM.

I admire the tinkerer too, but like Juliend ask what you want out of it. A stock 35mm carb, done up by RB, with head and decent port work, rev pipe, etc would out perform an otherwise stock engine with a 38 on it.

Surprisingly the carb fits the airbox boot and inlet rubber (inlet rubber will need lip filed off to suit larger carb), just not at the same time (16mm shorter) so I will make an adapter up at work this week!

Only other interference is the 2-stroke pump (which had been left benign but I hadn't removed), so I will have to make a blanking plate for that also!

i wanting to see it the carb actually helps..... nice work on the adapter!

that adapters looking good, you'll have to fling some mud on it to match it in, i recon that carb will pick up a few ponies your new ignition is letting it rev out nicer though its still getting a bit stifled up top, i'm sure theres a powerband hidden in them kdx's somewhere while still keeping decent bottom end ;)

In my box of jets so far I have

slow -
48
45x2


main -
162
130
170
165
160
120
145
190
150
160
140

to try and get it running

currently I think it has 50 slow jet and 200 main... its running REALLY RICH!

And this to go by

http://www.jetsrus.com/carburetor/carb_ ... parts.html

I have nothing between the 170 - 190 mark

you do know your gonna have to lean that carb WAY out to get it to run, right.

Even with the right jets, you still may need a slide and a needle to really get it right. Your pilot's are right in range I'd venture to guess. I'd try your 165 main....Gotta do plug chops though!!!

What pipe are you running?

Does this carb have a TPS triggered powerjet on it?

The carb is electronic free, standard jetting for this carb is 50/175, managed to get the idle nice on the 48, and am awaiting the 180 main to show up.

I fitted the needle from my PWK (it was one of the ones you guys recommend), I was surprised to find the needle in it was in the top clip position (leanest) bearing in mind how obscenely rich the rest of the jetting was, but for now I am in the 3rd position, pilot jet is sorted, next is the main, then finally needle.

Pipe at the moment is a "proskill" pipe, they seem to be made only in thailand, not a very tasty bit of kit... when the money arises, I will be investing in a desert style pipe.

Currently @

Pilot - 48
Needle - 3rd clip (i think it is CEK)
Main - 170

How's it acting?

[img::]http://s4.postimage.org/4z54vpckf/image.jpg[/img]

Seems to run best so far with needle on top clip, so a leaner slider is required. Yet to take her for a spin (thats what tomorrow is about :D), but the response when revving her up standing is amazing compared to the PWK, 16mm shorter seems to make a difference! Will only know for certain when I get it to the playground though.

Holy ****!

So far I'm on,

48
CEL top clip/#6 slide
180

and the bike is explosive, it has suffered a tiny bit low down, though if I really want low down, I'll put the 28mm carb back in.

Mid to top end is absolutely on fire, this carb is an amazing improvement over the PWK35/36 (I'm yet to check the diameter right up close to the slide, tbh I don't really care), the response when the bike starts revving is awesome, I've been riding tight woody areas today and the snap is excellent, though the back end is kicking out more than usual (what do you expect really).

Going to go up and down 5 on the main and see what I get, but to be honest, I am completely stoked about getting it so close from the start and I will NEVER be looking at the PWK again!

AWESOME!

I have a crappy Tony Hawk's helmet cam somewhere, if I find it, perhaps next weekend I will strap it to my lid and see what you guys think! But I really must say, for £28.50 ($46) ebay win.... RESULT!!!!