02’CR250 baseline jetting tips needed


pontiac

Member
May 9, 2002
48
0
I just picked up a low hour 02’CR250 and would like to get some input on baseline jetting specs. I just received my manuals from Helm and they offer detailed jetting specs to start with, but I’d like to know any other tips that may help to keep things crisp from idle or WOT. The bike will be used purely for fun (mostly trail & some mx) at an altitude range of 3,000 to 4,000 ft with outside temperatures from 70F to 100F. The bike currently has a Boyesen RAD valve & Pro Circuit 296 canister with everything else being stock. The fuel being used is 91 octane pump swill mixed @ 40:1 with Mobil MX2T.

I’ve read comments on various forums about filing the bottom of the slide by 2mm, which reportedly improved the low end throttle response & power by a noticeable amount. Has anyone here done this? What kind of results did you get?

What jetting specs did you find worked best on your similarly configured 02’CR250 and what altitudes & temps were those specs based on?

Has anyone here dialed in their Mikuni as best possible, then installed the Keihin 38mm PWK Air Stryker carburetor to compare its performance? Is there a definite improvement with the Keihin carburetor? What kind of improvement did you notice? Is this a direct bolt on or will I need a different boot to make it look sano?

At some point in time I’ll be adding some flywheel weight (~10oz) to smooth out the power delivery and will have the cylinder ported Mo-Better Everywhere, but for now I just want to dial it in as is and have some fun with it.
 

Sandy Whoops

Member
Oct 11, 2003
74
0
At sea level, the '02 is a little fat in the bottom and lean on top. Complicating the issue is a lean spot at 1/4 throttle that can result in detonation.
Below are my current sea level / summer settings, which have been used up to about 1500'. Aside from a FMF TCII, the engine is stock.

Main - 400 (stock is 380)
Needle - 6BEY30-74 (stock)
Clip - 2nd or 3rd from top
Nozzle - S8 (stock is S9)
Pilot - 30 (stock is 32.5)
AS - adjusted per conditions, but about 2 turns out

At 1500' , the 400 main is a bit too fat. A 390 would be better.

I tried the S8 nozzle only after buying and testing a bunch of jets and needles. In retrospect, it's probably better to start with the S8 nozzle and jet to it.
Not sure how the Radvalve affects your carb. But I'd suggest you order an S8 (from Yamaha), a 390 main, a 30 pilot, and a 6BEY30-75. Look for crisp throttle response, no detonation at low RPMs @ 1/4 throttle, and overrev that won't quit. Tip: the clip position has a considerable impact on overrev - experiment.
 
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bedell99

~SPONSOR~
May 3, 2000
788
0
these are my settings. The best thing to do on an 02 is get a s8 nozzle from yamaha. I race and ride a 5000-6000 feet using TT111 leaded fuel. Sometimes I use Sunoco GT100 unleaded when I can't get the leaded stuff and have to raise my main to 360. (It is oxygenated). I ride in the upper ranges of the power band and run amsoil 40:1. I say this again I ride only motocross. I get no goop at all from my pipe and my plugs are always perfect. I know a couple of my friends run 340-350 mains and have good results but they ride a bit slower. I had riding buddy who was an A rider that used a 370 main and had no goop at all. The bikes jetting really depends on the rider. This bike like to be rev'd and rewards the people for doing it.


Main - 350(leaded)-360(unleaded) (stock is 380)
Needle - 6BEY30-76 6BEY30-74 (stock)
Clip - 1st or 2nd from top (Depends on track)
Nozzle - S8 (stock is S9) very important
Pilot - 30 (stock is 32.5)
AS - i like no idle and the bottom to be a bit fat.

I keep everything fresh in my engine and change the plug about once a month.

Erik
 

murphy's law

Member
Oct 11, 2002
47
0
here are my specs for summer whether (75-85F) at sea level-- Motocross only.
27.5 pilot
30-76 needle in 3rd pos
S-8 nozzle
360 main-----I wouldn't go this lean on the main jet with pump gas at your altitude.
motul 800 mixed 32:1 with vp c-12.
eric gorr mo better porting :)
v-force set on low tension.
stock pipe with fmf ti-2 silencer.
iI've never had a bike that is so sensitive to changes in whether. If i were smart i would keep a log of what worked in different conditions to keep from fumbling around every day.
 

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