Koso 34mm Carb?

[sanstoetter]

I'm in the process of rebuilding the engine on a new-to-me 93' KDX 200, and in the process I've found that it's running a Koso 34mm carb. (Pictures Below)
**Let me know if there are anymore pictures that would be beneficial**

Backstory:
I bought the bike running, but with transmission issues (5th Gear on the input shaft is locked up). It started up easily, idled well, revved well, but I could not run under load or WOT. From what I could tell the previous owner did not realize it had transmission issues when he bought it non-running, and once he got it going he bailed. I believe he was the one who installed this carb, and never had a chance to actually ride it.

Bike Specs:
1993 KDX 200
FMF Pipe/Silencer
Boyeson Power Reeds
Uni Cone Filter
Wiseco 66mm Piston

Questions:
1. Is there a way to identify the current size jets if they are not marked?
2. Do these jets look similar the the Keihin jets this carb is modeled after?
3. If the bike idled well with the current jetting will it suffice until the piston/rings are broken in?
4. Any suggestions on a base jetting to start with if I need to buy new jets?
5. Is this carb going to seriously hurt performance enough that it'd be worth a couple hundred to find a stock carb?

[youtube][/youtube]





The Hex is 8mm for scale

[newbbewb]

wow, looks like a PWK pilot and a CVK pilot. A chinese knock off of a cvk+pwk carb? WTF. Take that carb, cock back real hard, and throw it as far as you can.

As good as the factory PWK carb is in E series, buy a factory unit used, clean it up, jet it, ride wheelies.

I'm assuming you are the the lower 48 states, so with some looking around, a PWK shouldn't run more that $100 I wouldn't think.

[sanstoetter]

Im in central NC, but a quick ebay search showed them about $175. The Wiseco piston already threw me over budget... An extra $100 will probably set me back a month. I do eventually plan to buy a stock carb, and then send it to RB, but Id prefer to get riding once the motors together.

[newbbewb]

I understand wanting to ride right away, I do. That carb there, unless you have the top part where the needle and slide fit it, won't work. As far as the jetting and things go, good luck sir. I suppose I'd suggest you follow the jetting guide on this forum.

To answer your questions:

Questions:
1. Is there a way to identify the current size jets if they are not marked? No

2. Do these jets look similar the the Keihin jets this carb is modeled after? No. The jet on the right looks like a PWK pilot jet, the other one I'm thinking it looks like a pilot jet from Keihin CVK carb.

3. If the bike idled well with the current jetting will it suffice until the piston/rings are broken in? yes, if you plan on breaking in your bike idling. I've had no problems breaking in a number of nikaseal bikes idling them, but thats my experience.

4. Any suggestions on a base jetting to start with if I need to buy new jets? Since this is not a PWK, I couldn't venture a guess.

5. Is this carb going to seriously hurt performance enough that it'd be worth a couple hundred to find a stock carb? If it were mine, I'd be less worried about performance and more worried about consistency and reliability. A PWK will give you those three items. If you check craigslist I'm sure you can find one for less that $175.

I'll keep my eyes peeled for one, even a kdx220 carb.

[newbbewb]

http://www.ebay.com/itm/Keihin-PWK-36mm ... da&vxp=mtr

air striker for $88, that a fair bit better than the factory kdx200 carb

[sanstoetter]

I placed the order this morning before researching, and now I have a few questions. After looking at it closer I realized that it did not come with a cap. AM I going to need a KDX specific cap, or will any air striker cap work? Also, where should I start on jetting (155 main/45 slow)? Will the standard needle work, or will I need to buy another as well.

[newbbewb]

the airstriker should bolt right up. needle should be same or very similar to pwk 36. A kdx specific cap will probably make your life easier. You will need the spring as well. Do you not have the factory cap and throttle capable in your bike? 155/45 would probably be a good starting point depending on what needle you get/choose.

[sanstoetter]

Nope, the bike came with the koso carb installed without a filter.

[newbbewb]

I'll look, I might have extra setup. I'll be back....

[newbbewb]

Pics of current carb setup without gas tank on?

[sanstoetter]

I wish I could take photo's with the bike together, but I'm still waiting on quite a few parts so that I can reassemble.

Current engine photo


Bike as purchased


Best photos I have of carb installed

[newbbewb]

That looks like a factory top rubber piece. hopefully you just need the screw on top piece and spring maybe. can you take the top off the carb, pull the slide off and take a pic?

Did you win or buy it now on that airstriker carb? I have a few pieces but no top for a pwk :(

[sanstoetter]

I did win the auction for the PWK36, and ordered jets for it. I need to source the slide, cap, spring, jet needle, and the cable holder. The seller should have them in his shop, but he'd misplaced them. I'll take photos of the rest when I get home tonight.

[Jaguar]

Are you going to tune in the Koso first or just set it aside?

[newbbewb]

If you can get the matching guts from that carb you're set. If not, drop an email to RB with a pic of what you got.

BTW, that vid of your bike idling, it sounds lean to me.

[sanstoetter]

I've got the KOSO hooked up, and I just got a few pilot/main jets that are for the PWK carb. If they work I'll throw those in the KOSO for time being. Everywhere I've looked for the PWK36 parts... seems like it'll need another $100 to install. I also tried to figure out fitment of the PWK36, but the bowl hits on both the rear spring, and frame. So I kept looking, and finally found a PWK35 of a 94 KDX200. I plan to use that as my baseline once it's ready to ride. I started it up last night with the KOSO installed for the first session of break-in on the stand, and I plan to do the next as well. Hopefully the PWK35 will get here Saturday, and I'll use that for the final bit of break-in. Next week I'll be selling all of the extra parts hopefully, and recoup some of the money.

[newbbewb]

Not sure why it doesn't fit. I have an airstriker 36 on my kdx200e it fits great. Has the carb boot been cut?

[Julien D]

the KOSO is a hair smaller, so maybe the boot was changed to something that would match it. This thread prompted me to look into the KOSO carbs a bit. Looks like they are actually decent. I think if jetted properly it will work just fine.

[sanstoetter]

The PO used what looked like a radiator hose to connect the carb and RAD valve. When I tried to fit the PWK36 the bowl was touching both the frame, and on the rear spring. I may have been able to cut that hose to sit the carb closer, but I found a KDX PWK35 for cheaper than I could find the slide/spring/spring/needle/holder. The KOSO carb idled well, but I did not want to spend money for needles/jets since I really just wanted a factory setup eventually.

I'm reselling the A/S PWK36, and the Koso 34mm if anyones interested.

The bikes running with the PWK35 now, and I just finished breaking in the motor. The carb arrived with a 42 pilot jet, 152 main, and the idle screw was turned out 1.5 times. I bolted it on, and it seems to run like a charm.

I look like a goober/squid, but here's a quick video of 1st-3rd in my neighborhood.
[youtube][/youtube]

[newbbewb]

the koso I had 3 years ago was crap. Like tuning a dellorto carb. Mine HATED elevation change. Would probably work great for MX or flat track, not trail riding.

Glad to head you got a PWK and that you're ripping now. Your settings are spot on to mine at home, 231ft elevation.