01 cr250 jetting

well as the title says i need some confirmation on my jetting. this is my first 2stroke so bear with me if this stuff is actually normal. so anyways i got my bike a week ago and it needed new oil seals on the crank. i put those in today and took it for a run. what i found was that it was like riding a 40+ horsepower light switch (literally)... it would sputter and bog a bit and also blow a lot of smoke in the lows, start to clear up in the mids, and hit like a ton of bricks, and run really good near the top. its very close if not spot on to the jetting recommended in the manual for altitude and temperature and im running 32-1 mix. the bike has a pro circuit works pipe with an r304 shorty silencer. would this make a huge difference in the jetting?i know it needs more air in the low rpm. i was thinking to open up the air screw a bit. is this the correct move to make? or should i change the clip position on the needle?

also the silencer can has a major leak on the seam where it comes apart to get at the packing and its spitting oil all over my swingarm, rear tire, wheel, brake disc, brake caliper, and the inside of my side panel. i found that the o-ring or sealer stuff is gone on the bottom, how can i remedy this so it wont spit oil everywhere? short of using duck tape that is?:smirk: thanks a ton guys!!!:smirk:

What type of elevation are you riding at? Factory jetting?

I ride around 3000-5000ft and have my jetting as such:

172 main

45 pilot

stock needle and clip

It runs really well however, a bit on the rich side still. As far as your pre-mix is concerned, if it's non-synthetic, 40:1 is prolly a good ratio. I run a full synthetic at 50:1. The bottle also instructs 50:1. I think 32:1 is too much oil.

What type of elevation are you riding at? Factory jetting?

I ride around 3000-5000ft and have my jetting as such:

172 main

45 pilot

stock needle and clip

It runs really well however, a bit on the rich side still. As far as your pre-mix is concerned, if it's non-synthetic, 40:1 is prolly a good ratio. I run a full synthetic at 50:1. The bottle also instructs 50:1. I think 32:1 is too much oil.

his cr comes equipped with a mikuni.

to the OP, i dont know your elevation but i will give you a GREAT starting point on that bike, as we got my friends 01 running awesome.

we run at sea level to a couple hundred feet but in my opinion, elevation doesnt make anywhere near as big of a change in jetting as temperatures do (until you start to really get up there). so id say if youre riding at 1000' or less with temps 60-80, this will give you a good start.

start with:

30 pilot

needle 2nd clip, stock

s7 nozzle/needle jet from his 97 yz125 (you can order these online)

410 main

air screw 1-1.75

what we ended up with on my friends 01 cr250 with a pc plat pipe:

27.5 pilot

needle 1st clip, stock

s7 nozzle

390-410 main depending on conditions

in our experience, the biggest change was from the nozzle and needle clip changes. he has no spooge with the stock mikuni carb that people always complain about. either way, id start richer and work your way down as noted above.

im at about 4500 feet. i believe that the main jet is the proper size as it runs almost perfect past the mid range rpms. i was wondering if i needed to adjust my air screw, slowjet, or needle clip or any combination thereof. and i am running honda hp2 premix which is 100% synthetic. the manual recommends running 32-1 as does the bottle... i know that if i changed the ratios it would affect the jetting but what kind of effect would less oil have on the engine?

What type of elevation are you riding at? Factory jetting?

I ride around 3000-5000ft and have my jetting as such:

172 main

45 pilot

stock needle and clip

It runs really well however, a bit on the rich side still. As far as your pre-mix is concerned, if it's non-synthetic, 40:1 is prolly a good ratio. I run a full synthetic at 50:1. The bottle also instructs 50:1. I think 32:1 is too much oil.

mynewcr250 is right. i have a mikuni not a keihin carb. from what i hear jetting the mikuni is a bit trickier.

Is the 2000 the only one with the PWK?

Is the 2000 the only one with the PWK?

99 and 00. same carb.

99 used 1370dka needle, and different pilot and main jets.

00 used the 715 triple taper needle, 48p and 180m. you can see the changes i made to my 00 in my sig.

to the OP, im having a hard time believing the stock 420 is the proper size main jet at that altitude. have you plug chopped it with a new plug? at that altitude you should be running leaner across the whole board...

also dont confuse running clean past midrange rpms as a sign of having a proper main jet. jetting is throttle dependent, not rpm dependent.

if you have an area where you can do a proper plug chop with a new plug, after 1 or 2 WOT runs you should have a mixture ring that resembles this (im actually gonna throw in a 175 next trip. been slacking due to the 40mph winds out in the desert lately)

http://www.thumpertalk.com/forum/showpost.php?p=10326481&postcount=5

to the OP, im having a hard time believing the stock 420 is the proper size main jet at that altitude. have you plug chopped it with a new plug? at that altitude you should be running leaner across the whole board...

also dont confuse running clean past midrange rpms as a sign of having a proper main jet. jetting is throttle dependent, not rpm dependent.

if you have an area where you can do a proper plug chop with a new plug, after 1 or 2 WOT runs you should have a mixture ring that resembles this (im actually gonna throw in a 175 next trip. been slacking due to the 40mph winds out in the desert lately)

http://www.thumpertalk.com/forum/showpost.php?p=10326481&postcount=5

nononono.... haha. im definatly not running the standard setting.:smirk: im running pretty close to the settings recommended in the manual for my altitude and temperature. 400 main is reccomended. but i am running a 380 or 390 right now im pretty sure its a 380 though, the needle clip is in 2nd position slow jet is a 35 and air screw is 2.5 turns out from bottom. sorry for any confusion. hahaha... and i have not done a plug chop. to do that you let it warm up, put it in a higher gear and give it WOT on a long flat straight and then pull the clutch in and hit the killswitch, right?
nononono.... haha. im definatly not running the standard setting.:smirk: im running pretty close to the settings recommended in the manual for my altitude and temperature. 400 main is reccomended. but i am running a 380 or 390 right now im pretty sure its a 380 though, the needle clip is in 2nd position slow jet is a 35 and air screw is 2.5 turns out from bottom. sorry for any confusion. hahaha... and i have not done a plug chop. to do that you let it warm up, put it in a higher gear and give it WOT on a long flat straight and then pull the clutch in and hit the killswitch, right?
LOL my fault. I assumed something and ran with it. sorry about that.

one thing sticks out tho. that pilot. I would try at a minimum a 30 pilot which I believe is 2 steps leaner for the mikuni. I think you are loading up when you're off the throttle and then when you give it gas its gotta clear out before it picks up proper. I've never ridden that high up but I wouldn't hesitate to still run an s7 nozzle and the stock needle in the first clip with a 30pj.

you've got the idea of the plug chop. you want to warm up on an old plug, swap in the new one and from the get go you want to go wot through the gears until you get up to 4th or so. other gears will work as long as they'll put a load on the engine for a bit. kill it as you said above and then pull the plug and chop em like I showed above. the mixture ring is what you're looking at. you want one with roughly the same diameter shown maybe a tad darker for safety sake. a new plug wont color quickly but the mixture ring will. that picture is a plug with two 5-7 second runs (5-7 secs in 4th gear).

32:1 is fine, and you can use a much less expensive oil with great results. Spooge is not cause by your ratio--it is the jetting that causes the problems. I used Yamalube 2R for years in mine, and pistons came out perfect. Lately I been running the Lucas semi-synthetic stuff in my current bikes with good results. It is only about $6 per quart at autoparts stores. Be wary of suggestions to run lean oil ratios. The engineers who designed the bike specified 32:1, and they know more than we do.

Regarding your jetting, unfortunately you have one of, if not the most difficult Japanese 250s to jet. I messed with my 01 forever. I got it to run well on the MX track, but it never ran right in the woods. I finally broke down and bought a JD jetting kit, and the bike was instantly transformed into the best and cleaning running smoker I've ever had. It ran so well at low speeds that I could putt putt around for hours with my 6 year old son on his XR 50, but it still ran great at race pace. Others have reported here that the real fix is carb replacement, but the JD kit is worth trying for $75 or so.

Regarding pipes, my 01 came with 2 pipes and 3 silencers (stock, fmf, pc). I used to mix and match them all the time, and never really noticed any difference in power or jetting requirements.

If you still find the bike has a "light switch" powerband (you must be coming off a 4 stroke! You need to try a 125!) after you get the jetting sorted, try a 12 oz FWW. I bought one for woods riding, but I liked it so much that I just left it on for everything.

Edited by rpt50
sp

before you go any father check your power valve operation, if it is stuck open it will not have any bottomend. alot of these old bike the power valve gets stick or people gets the linkages wrong. Anyway just take the plug out of the left side of the cylinder and rev the bike to see if it goes from the L mark to the H mark. Make sure the power valve is working then get the jetting fixed.

I think if you've done any research you'll find that the stock jetting is considered rich by most, maybe even way rich. In the MXA secret jetting spec's article you'll find they went leaner from stock in many ways....http://www.motocrossactionmag.com/Reviews/News/MXAS-SECRET-JETTING-SPECSDEC-3-2003-4308.aspx

01 CR 250 stock vs. MXA

Main=420 vs. MXA=430 this is the only area where they went richer and it may be due to some of the other changes they made.

.

Pilot=35 vs. MXA=30 which is 2 steps leaner. The pilot will affect 0-1/4 throttle with the biggest influence @ idle.

Needle=6BEH1-73 in clip #3 vs. MXA=6BEH2-75 in clip#2 this amounts to 2 diameters leaner and 1/2 clip position leaner. The diameter change will affect 0-1/4 throttle with the biggest influence prior to 1/8 throttle. The clip position will affect from @ 0-7/8 throttle with the greatest influence in the area of 1/4 to 1/2 throttle.

Slide=#4.0 vs. MXA=#5.0 which is 2 steps leaner. The slide cut-away affects 0-3/8 throttle with the biggest influence @ 1/8 throttle.

JD's kit for the 01' comes with a much leaner nozzle, stock was an S-9, his kit contains a leaner S-4. The nozzle will affect the area from @ 0-7/8 throttle.

Again I think most any research you do in regards to the stock settings will turn up the need for leaner jetting. My experience with the stock parts was minimal before installing the JD kit. However I didn't find perfection with the JD kit either, so I tried the stock needle in combination with the JD S-4 nozzle. This may have been the best combination I tried in the Mikuni prior to receiving/installing a used PWK. I say "may have been" because I only tried it once before changing to the highly touted PWK.

Currently the PWK set up that were running may be as good as the last Mikuni set-up but I can't honestly say it's better until we do a back to back comparison. FWIW in any of those configurations (stock, JD kit, JD nozzle & stock needle, and the PWK) the motor has continued to produce a spooge trail that runs down the silencer and drips onto the caliper.

Most of our riding occurs between 5,000' and 10,000' with temps ranging from 50 to 90 degrees, some track but mostly trail. Here's what I felt worked best for us with the different configurations.

JD kit= a 370 main, 25 pilot, red needle shimmed to = clip position 2.5, stock 4.0 slide.

S-4 nozzle with the stock 6BEH1-73= a 370 main, 25 pilot, clip position #2, stock 4.0 slide.

PWK= a 168 main, 38 pilot, 1370DKA needle in clip #2, #7 slide.

I run a s-8 nozzle 410 main, 32.5 pilot, stock needle, work great on the 01. Runs perfect. You guys are in altitude so you can go leaner on nozzle and be safe. Where I am at would not go leaner than above settings.

wow guys... thanks alot for all the advice. :ride::lol: its very overcast, cold, and a bit rainy today. so if the wether is better tomorrow i will test the power valve before i mess around with the jetting just to be sure. but when i got the bike i took the top end off to clean the power valve and check the piston and cylinder. so im almost 100% sure thats not a problem. i ordered a jd jetting kit last week because the bike did not come with any other jets other than what was in it, and i heard this was the best route to go for the 01 cr250's it should be here tomorrow too. so if its not the power valve causing the problem ill mess around with the jetting. yes rpt50 this is my first 2stroke. cant really afford the maintenance on any thumper except for a trail bike. plus i wanted the simplicity of a 2 stroke so i could easily do maintenance myself.

I think if you've done any research you'll find that the stock jetting is considered rich by most, maybe even way rich. In the MXA secret jetting spec's article you'll find they went leaner from stock in many ways....http://www.motocrossactionmag.com/Reviews/News/MXAS-SECRET-JETTING-SPECSDEC-3-2003-4308.aspx

01 CR 250 stock vs. MXA

Main=420 vs. MXA=430 this is the only area where they went richer and it may be due to some of the other changes they made.

.

Pilot=35 vs. MXA=30 which is 2 steps leaner. The pilot will affect 0-1/4 throttle with the biggest influence @ idle.

Needle=6BEH1-73 in clip #3 vs. MXA=6BEH2-75 in clip#2 this amounts to 2 diameters leaner and 1/2 clip position leaner. The diameter change will affect 0-1/4 throttle with the biggest influence prior to 1/8 throttle. The clip position will affect from @ 0-7/8 throttle with the greatest influence in the area of 1/4 to 1/2 throttle.

Slide=#4.0 vs. MXA=#5.0 which is 2 steps leaner. The slide cut-away affects 0-3/8 throttle with the biggest influence @ 1/8 throttle.

JD's kit for the 01' comes with a much leaner nozzle, stock was an S-9, his kit contains a leaner S-4. The nozzle will affect the area from @ 0-7/8 throttle.

Again I think most any research you do in regards to the stock settings will turn up the need for leaner jetting. My experience with the stock parts was minimal before installing the JD kit. However I didn't find perfection with the JD kit either, so I tried the stock needle in combination with the JD S-4 nozzle. This may have been the best combination I tried in the Mikuni prior to receiving/installing a used PWK. I say "may have been" because I only tried it once before changing to the highly touted PWK.

Currently the PWK set up that were running may be as good as the last Mikuni set-up but I can't honestly say it's better until we do a back to back comparison. FWIW in any of those configurations (stock, JD kit, JD nozzle & stock needle, and the PWK) the motor has continued to produce a spooge trail that runs down the silencer and drips onto the caliper.

Most of our riding occurs between 5,000' and 10,000' with temps ranging from 50 to 90 degrees, some track but mostly trail. Here's what I felt worked best for us with the different configurations.

JD kit= a 370 main, 25 pilot, red needle shimmed to = clip position 2.5, stock 4.0 slide.

S-4 nozzle with the stock 6BEH1-73= a 370 main, 25 pilot, clip position #2, stock 4.0 slide.

PWK= a 168 main, 38 pilot, 1370DKA needle in clip #2, #7 slide.

For your settings in Colorado what spark plug and what oil mix?

For your settings in Colorado what spark plug and what oil mix?

BR8ES or BR8EG and Mobil-1 racing 2T with pump premium at 32:1.

BR8ES or BR8EG and Mobil-1 racing 2T with pump premium at 32:1.

thanks im running amsoil at 50:1 so I may need go a little leaner the guy that had it before me was running a 32.5 pilot 370 main shees a little fat on the bottom for sure

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