Keihin Carb. Test/Write up

[Red Rocket #13]

Being the person that I am, I wasnt so happy with how my '03 CR250 ran. I know for a fact that some of you out there have got the time, the money, and the equipement to spend on your Mikuni carburator. I also know that some of you have gotten your carb to run great. Thats awsome, and I must applaud your efforts, but I have tried every thing with the Mikuni and it was all to no avail. I had lean spots, there was a certain studder off idle, and truthfuly, thats the best I could get it to run.
Well after coming to this great community looking for help with jetting I learned of a ever growing group of people that have coughed up the 219$ to buy a Keihin carburator. I was rederected to a forum in the dirtrider.net socials and found that many many people have done this with almost perfect success. Well im no money bags, and people who know me say I'm cheap, but I went ahead and earned that 219$ so i could ride my CR250 and like it. This little write up is my experience with the new carb so far, and my opinion.
After doing alittle research, and asking a few questions of course, I found the carb that I needed. It is a Keihin PWK Airstryker Quad Vent 38mm. This little mouth full also comes stock on all 2000 CR250s. You can get it at numerous places incuding your local shop if you so choose. I hunted around for awhile and finaly decided to order it from a good friends shop a couple miles away from me. I asked him about the jets and every thing, and it already comes with jets, a slide, and a needle with the E clip. So basicaly put, I got a full carburator with out having to put in a special order.

Stock Jets (the ones that were in there when I whiped open the package)
Main: 170
Pilot: 55
Slide: # 7
Needle: DDJ
Clip Pos.: 2nd groove

Once I recieved my carb, I also bought some suggested jets, and a different needle. Not every one is gunna need a different needle, but I did so I bought one. I picked up a #168 and 172 main, a #42 and 40 pilot, and the #1369 needle. I also had to change the float level to 16mm (stock), to learn how to do this go here - How to Set Your Float Level
After every thing was where it needed to be, I had to try it out. For the very first test I used all the jets that came with the carb originaly. After taking the Mikuni off, the new one bolted up easily, it uses all the same boots, the same cable, so theres no need to worry. One thing though, the Keihin is a slightly tighter fit in the intake boot, but to fix this just loosen the clamp alittle more. After bolting the carb up, the last thing I had to do was put the fuel line onto the carb. Right away I noticed that the fuel line's inner diameter is alittle to big for the carb. To test to see if it leaked I turned the fuel on, and sure enough it leaks. To fix this little delima, I used a tube clamp (like the ones on the radiator hoses, yet smaller) and the problem was gone. After messing around with the air screw and idle screw I got it to run decently.
First test ride
I needed to put either the 42 or 40 pilot in, since it would bog to the point of almost dieing, yet the top end was noticably strong. After I installed the # 42 pilot, the bike would revv uncontrolably so I turned down the throttle screw and the air screw to accomodate the pilot jet.

Second test ride (W/ #42 Pilot)
Probably the most noticable of the changes I made. Indeed I was on the right track to having this thing perfect. Right now, theres no bogging, no hesitations, and no lean spots. There's still quite a bit of smoke, and its blowing alot of spooge out the silencer. Im now going to put the #40 pilot in. Right now, im happy with the way it runs, yet I can make it better.

Third ride (W/ #40 Pilot)
More noticable power in the bottom, better throttle responce, and over all a better machine. Still smoking and still spooging (DOH!)

Final modification - The new needle
When I decided to put the needle in, all I had to do was unscrew the slide top, which was a snap compared to the Mikuni. The process took me a matter of about a minute to put the needle in, which I was happy for. The bike seemed to run alittle lean, but 1 turn in (1 turn out now) on the airscrew corrected that. As of right now, theres little to no smoke, and best of all, BARELY ANY SPOOGE!.

Performance
On the performance side of things, it runs way better, due to better carburation, but no big time horsey gains.

Ratings
Simplicity: 10/10
Value: 10/10
Performance: 9/10 (Theres not quite as much top end over rev as there used to be)
Over All: 9.8/10

My final opinion on this conversion is: I wish I would have done it sooner. No joke people, this is the real deal for any one with jetting problems on their '02-'03 CR250. This modification has changed my poor, blubbering machine into a pure bred race weapon. I suggest this carb to any one with a '02-'03 CR250, even if they think they have it dialed. The Keihin is a snap to work on, with a bottle type, screw on slide lid, and easy maintenance internals. After spending tons of money on jets for the mikuni to no aid, then switching to this carb, I can fully tell you it was well worth the 219$ I spent on it. Now that I have tested it, I would have paid more, its that good. As you can see Im totaly thrilled with the carb and Id like to thank all of you people for your help, particulary Faded. Thanx Every one and I hope this helps people who are interested in doing this.

Red Rocket #13

[nappers]

Very nice write up! thanks for posting. I'm sure many will benefit, even if it is a different bike. They may be having similiar problems.

Now that you got it dialed in, go out and ride that sucker like no other!

[Faded]

Bump to the top.

I didn't even see this posted, way to go Red. I'm glad it's working out for you. I have two very limited rides on mine, but it looks good so far.

[Red Rocket #13]

oh so u finaly got it on there faded? sweet action man. Let me know what u think of it. Well adios.
RED OUT

[Aus_Rider_22]

That was a very well written review! A joy to read!
Glad you got it sorted and are happy with your new carby!!

[ossagp]

Now,,want your 2003 to feel more like a 2000? Use the crank that the 2000 does. I think Wiseco will see you one for under 180.

[Woody_393]

Wow, very nice write up indeed.

I think this is KB info. Agree'd?

[Red Rocket #13]

KB? Not sure what that is......but, the crank will make a difference? heavier? lighter? i dunno tho, i like the way it rides as is, now that i also got a sst pipe .... but i might look into it

[Woody_393]

KB = Knowledge Base

[Red Rocket #13]

Ohh i c.
Well ill let u peeps do that, by the way thanx for the positives every one, its cool u people appreciate that, do with it wat u will

[Woody_393]

copied

[Pretendo]

I had the same success with the 2002 RM-125... i switched to a keihin 250 carb from a 97 RM-250 and it was worlds better. I was very satisfied, and i dont even have it jetted perfect yet. + the Mikuni jets arnt even accurate... i have a jet guage and the jets wernt even consistent. I think some of the performance could have came from the longer barrel, but who knows, i love it.

[johncam25]

Great write up. I have a 03 Blaster with a 28mm Keihin. I can't get it to run. Do you have any ideas. I have tried a #135, 165, and 235 Main. The pilot is a #38 I was going to try a #55 but I think its to big.

Thanks

[Pretendo]

the bike gets good spark? are you sure its the fuel circuit? im not to sure about the yamaha blaster, normally only dealing with dirtbikes, but its pretty much the same exact thing. what does stock specs show the jetting should be. id try that and work from there, unless u have a differant size carb, which i donot know what comes stock. give a little more ifo and i may be able to help.

[johncam25]

Originally Posted by Pretendo

the bike gets good spark? are you sure its the fuel circuit? im not to sure about the yamaha blaster, normally only dealing with dirtbikes, but its pretty much the same exact thing. what does stock specs show the jetting should be. id try that and work from there, unless u have a differant size carb, which i donot know what comes stock. give a little more ifo and i may be able to help.

It has good spark. No, not to sure its the fuel circuit. Stock is a 26mm, I'm using a 28mm. I think it might be the timing. I have no clue how to change it. I just put a new stator, and thats the only place it looks like i can change the timing.

thanks

[kilbuck455]

just did the carb swap on my 06 so far so good lost a little snap though. but no more jetting headaches. Glad i did it

[hondatwosmoker]

I have an 03 Cr 250 and Im just about to spend the money to buy a kehin carb because I am so frustrated with the mikuni! Ive heard from two people now the with the switch you do lose some snap. Is this true?? Very nice right up red rocket. easy to read and persuasive. I hope I have similar success.