Mikuni carb 02-04 CR250

[SQUIRLEYMOFO]

I did a search and found a lot of people switching to the Keihin from the 2000 and 2001. Most of the posts were a couple of years old. Has anyone had sucess jetting the Mikuni are is the "hot" setup still the older carb?

 

[CR Swade]

James Dean supposedly has a Mikuni jetting kit that works well. I always used a Keihin on my 02 w/ excellent results so I can only vouch for the PWK. Give James Dean a call at JD Jetting and he should be able to help.

 

[rcpilot_971]

I did a search and found a lot of people switching to the Keihin from the 2000 and 2001. Most of the posts were a couple of years old. Has anyone had sucess jetting the Mikuni are is the "hot" setup still the older carb?

I just finished putting a pwk on my o2 cr250 like 10min ago kind of a pain to put on have not got to ride it yet I hope it runs good with the stock jetting I would hate to have to pull it off again had to take the sub frame off and then had to take the air box off the sub frame still would not go right on had to work it a little

Tim

 

[mx547]

i made the switch. i didn't have any trouble getting it in there and didn't have to take anything off. i'm running stock jetting and its close. its nice to have that problem out of the way. get the keihin and spend your time riding instead of messing with carbs.

the 2001 had the mikuni.

 

[mylesc]

I just finished putting a pwk on my o2 cr250 like 10min ago kind of a pain to put on have not got to ride it yet I hope it runs good with the stock jetting I would hate to have to pull it off again had to take the sub frame off and then had to take the air box off the sub frame still would not go right on had to work it a little

Tim

rcpilot_971,

To rejet your carb, you don't need to pull it off again. If you need to change out the main or the pilot jets, disconnect the fuel line and remove the slide/top cap assembly. Drain the float bowl. Loosen the clamps and rotate the carb until you have access to the float bowl. It's a bit tight on the aluminum framed CR's but once you do it, it's not so bad.

 

[rcpilot_971]

rcpilot_971,

To rejet your carb, you don't need to pull it off again. If you need to change out the main or the pilot jets, disconnect the fuel line and remove the slide/top cap assembly. Drain the float bowl. Loosen the clamps and rotate the carb until you have access to the float bowl. It's a bit tight on the aluminum framed CR's but once you do it, it's not so bad.

Yea I know I meant I hope it runs good enough to go riding and I would not have to put the mikuni back on as I did not have any jets for the pwk but I do now so it should be no problem


Tim

 

[rcpilot_971]

i made the switch. i didn't have any trouble getting it in there and didn't have to take anything off. i'm running stock jetting and its close. its nice to have that problem out of the way. get the keihin and spend your time riding instead of messing with carbs.

the 2001 had the mikuni.

MX 547 you say the stock jetting is close are you at sea levle
and is your bike stock ??

 

[mx547]

600 ft. stock except for boysen reeds and dep pipe and silencer. its a little rich in the midrange but pretty good on top (which is the part i care about). i'll probably just leave it that way for now.

 

[mtk]

rcpilot_971,

To rejet your carb, you don't need to pull it off again. If you need to change out the main or the pilot jets, disconnect the fuel line and remove the slide/top cap assembly. Drain the float bowl. Loosen the clamps and rotate the carb until you have access to the float bowl. It's a bit tight on the aluminum framed CR's but once you do it, it's not so bad.

You don't even need to do all that, at least for main jet changes. Skip removing the fuel line and simply turn off the petcock. Stuff a rag under the float bowl and then remove the large hex plug in the middle of the float bowl, draining the bowl and exposing the main jet. Remove the main jet with a 6mm wrench and reverse the process.

Slow jet changes require carb removal, but I found that to be relatively simple as well. Unbolt the silencer mounting bolts (so you don't have to mess with the pipe/subframe connection), loosen the airboot clamp, and then unbolt the three subframe mounting bolts. Remove the subframe, with airbox attached, and then you can pull the carb out, after you remove the top of the carb and the slide.

I've been much happier with the PWK than with the stock Mikuni on my 2002.

As for jetting, my 2002 has been Mo Betta ported by Eric Gorr, so that changes things a bit. But with that said, I'm running WAY leaner jets in my 2002 CR250 with the PWK than that same carb used on my 2000 CR250 engine.

 

[soulmate33]

You don't even need to do all that, at least for main jet changes. Skip removing the fuel line and simply turn off the petcock. Stuff a rag under the float bowl and then remove the large hex plug in the middle of the float bowl, draining the bowl and exposing the main jet. Remove the main jet with a 6mm wrench and reverse the process.

Slow jet changes require carb removal, but I found that to be relatively simple as well. Unbolt the silencer mounting bolts (so you don't have to mess with the pipe/subframe connection), loosen the airboot clamp, and then unbolt the three subframe mounting bolts. Remove the subframe, with airbox attached, and then you can pull the carb out, after you remove the top of the carb and the slide.

I've been much happier with the PWK than with the stock Mikuni on my 2002.

As for jetting, my 2002 has been Mo Betta ported by Eric Gorr, so that changes things a bit. But with that said, I'm running WAY leaner jets in my 2002 CR250 with the PWK than that same carb used on my 2000 CR250 engine.

What kind of jetting are you running now?
What kinds of differences in performance with the porting?

 

[skipn8r]

Slow jet changes require carb removal, but I found that to be relatively simple as well. Unbolt the silencer mounting bolts (so you don't have to mess with the pipe/subframe connection), loosen the airboot clamp, and then unbolt the three subframe mounting bolts. Remove the subframe, with airbox attached, and then you can pull the carb out, after you remove the top of the carb and the slide.

I just changed out my slow jet a few days ago by removing the chaing guard, loosening the carb clamps and rotating the bottom out to the side; I didn't even remove the slide. Once you rotate the bottom out, remove the four bowl screws, remove the bowl and there you go. About a 15 minute job.

 

[mtk]

I couldn't get mine to rotate enough to do that myself. I also found that pulling the slide allowed it to rotate more freely in the boot. I was also concerned about kinking the throttle cable since that results in VERY BAD THINGS happening.

As for jetting and performance, I'm running a 162 main jet, 38 slow jet, air screw ~1.5 turns, and an R1368NS (CR500) needle on the 3rd clip in the bike right now. Performance-wise, the bike runs fantastic. It pulls hard from the bottom and builds pretty smoothly to a nice top end rush. When I had the top end ported, I also changed from a ProCircuit pipe to an FMF Fatty/PowerCoreII combo w/E-line pipe guard and also installed the PWK at that time so I changed a lot of variables at once, making it hard to pinpoint what mod did what. Getting back to jetting, next summer I'll be trying a 160 main and a 35 slow to see how they work, assuming I don't get a 265cc big bore kit before then and have to start all over again jetting-wise.

 

[soulmate33]

As for jetting and performance, I'm running a 162 main jet, 38 slow jet, air screw ~1.5 turns, and an R1368NS (CR500) needle on the 3rd clip in the bike right now.

Glad to hear that the porting is running well. It has been mentioned that a jetting reduction will probably be required after porting.
I'm just really surprised that you can go as low as a 38 pilot. I'm running a 45 pilot at ~1.5 turns. This is at sea level here in Hawaii with humidity @ 65%-85%.
Were you doing plug chops to get down to the 162 main? I'm running a 175 main.
Did you try the stock 2000 CR250 (A715/289R/A327/A487)needle?
Or do you find that the R1368NS needle runs alot better?
I'm still contemplating doing a big bore or just a port job.

 

[mtk]

I tried the stock needle and found I needed the smaller straight section of the R1368NS needle. If I had the complete assortment of 2000 needles that Honda sold I'm sure I could have found a triple-taper needle that worked.

As for jetting, Faded put a PWK on his CR265 (also Mo Betta ported) and he was running jetting in the same ballpark as me. Make that I'm running the same as him since he did his first. I've tried lots of different jetting combinations and I'm sure that a larger main would be way too fat on this engine. I'm also sure the 38 slow jet is too large for this set-up and will be trying a 35 whenever I can ride again (probably spring). The 38 is close, but still too rich.

I'm also running Sunoco Supreme race gas (CAM2 "blue") mixed at 32:1 with Mobil MX2T. Mine was supposed to be set-up for pump gas by EG but I was getting a bit of detonation when running on 93 Super (with MX2T) so I switched to CAM2. Yes, I know VP is better race fuel, but CAM2 is half the price and I'm only trail riding the bike. I'll pay $4.99/gal for my playtoys but $9/gal is a bit much. Since I've already bit the race gas bullet I'll probably send my head back to EG to have the compression bumped up slightly to take full advantage of it. Or maybe I'll wait until I go the full 265cc route to get the compression changed.