KDXRIDER.NET

I am thinking about getting a Keihin 38 mm for my KDX220. Has anyone tried this before?

I don't think the diameter will fit the boot or the airbox. I think a 36 is a large as it will go. Measure your rubber to see how big you can fit.

Yes you can shoe horn in a 38 mm carb into the KDX 200. It is a very tight fit, but with lots of cussing and sore fingers it will go in. I'm not sure on how long the carb boots will last without cracking or tearing.

This set up never made it to the dyno and had only promising results in field testing. We kind of lost interest in the project and the bike has sat for years now (owner lost interest).

We did learn that it was going to take a lot of tuning it make it right, but pulling the carb on and off so many times, the interest died.

Ron

Might not be too bad on the motor, but would kill bottom end over a 36. I actually prefer the smaller carb on my 250 over the 38. More useable overall mower when not riding MX. Also, The 36mm PWK is the same body as a 38....Think it's designated as a 36-41 body. That's why RB Designs bores the 35mm's to 36. The 35mm shares the body w/ the 33. Looking at this chart: http://www.sudco.com/vol33/125-128.pdf It appears that the larger body is 3cm longer which would be the biggest concern regarding fit.

Edit...OOPS Ron chimed in while I was typing.

What is it you are after...or think you're after..with a 38?

canyncarvr,

I own and ride a KX 250; when got the KDX I inmediately felt the big power difference (as expected). So, to answer your question, I am looking for more power.

Here is why I think it might work:

1- Most 125 MX and the KTM 200 come stock with 38 MM carbs.
2- Installing the 38 mm will give less low end power on the KDX but I firmly believe that if I have the carb modified by Ron I can haved a good combination of power and low end response.
3- I think in terms of money, getting a 38 mm on ebay will be easy and the gains in performace significant.

My only issue now is to measure if a 38mm carb will really fit on the KDX.

Re: 'My only issue now is to measure if a 38mm carb will really fit on the KDX.'

That's...'issue was...', right? Now, I mean.

There's a lot more to how an engine runs than displacement. Compare the two KDX models (200/220) for an excellent example of that. I'm not sure where the idea came from that a KDX220 has anything to do with a KX or MX anything. It doesn't.

The 220 was designed to be a low-range puller..that's why it comes with the 33mm carb and why the port timing is different. Sure, it can be improved to run better than it does out of the box...that's true of any bike, even the 'race ready' ones.

As far as the punkin 200s with a 38mm...take note of where they rev to. They don't get to that point just 'cuz they can suck more air.

Still, it would be interesting what the outcome is. Let us know how it turns out!

Good luck!

Look at the link I provided for measurements.

a 35 bored to 36 will feed plenty.

Porting and head mods for race gas will net the largest power gain.

Mid 90's KX125's used a 365mm carb I think. Always wondered why people did not install those, flat slide and all....

I think KTM is back to the 36 for all the EXC models....For a while it was just the 300.

fuzzy,

Yeap, you are correct. Even the 300 comes with a 36 mm nowadays, interesting... see below:


Engine type Single cylinder, 2-stroke
Displacement 293.15 cc
Bore x stroke 72 x 72 mm (2.83" x 2.83")
Starter Kickstarter and e-start
Transmission 5 gears wide-ratio
Carburetor Keihin PWK 36 S AG
Control TVC twin valve control
Lubrication Mixture oil lubrication 1:60
Transmission lubrication 15W50
Primary drive 26:72
Final drive 13:50
Cooling Liquid cooled
Clutch Wet multi-disc clutch, operated hydraulically
Ignition Kokusan digital E

My kid's YZ125 has a 38mm Mikuni carb. That bike will slaughter mine on the track. In the woods, he always tries to come up with some excuse on why his bike ain't running right and we need to trade. hmm, I wonder if Ron would put his divider plate in the YZ carb...

Colorado Mike,

I think Ron should be able to add the divider in your 38MM carb... on his web site he says he works on almost all types of carburetors.

I'm sure it would help, but a 125 is what it is.....Not really intended for woods.

If you were gonna go RB for the 125 I'd say get a 36mm TM off ebay, and have ron go through that. Then just swap carbs real quick for woods work. The smaller carb would net the best low-end improvment without going inside the motor. As mentioned the 36/38 have the same body, and you could swap carbs in 5mins...