2002 CR250 Jetting/Carb Setting Question

[gpconcepts]

Hello Barfers,

I have a 2002 CR250. I recently replaced the problematic Mikuni carb with a new Keihin replacement from Carb Parts Warehouse. It came set up with a 172 main, 48 pilot, needle on the middle clip and the air screw set to 2.5 turns out. While it runs with these settings, the bike is impossible to kick start and will only start at all if I bump start it. Kick starting is never successful, whether hot or cold. Once running, symptoms also include:

- While on long descents with the throttle closed, the engine dies and struggles to restart when I apply the throttle. I have to pull in the clutch and blip the throttle as I go downhill to keep the engine running for fear of getting stuck.

- Engine will not idle regardless of where the idle screw is set.

I have since dropped the pilot to 45 and raised the main to a 178 based upon FMF recommendations. I’ve also tried moving the air screw between 1.5 and 2.5 turns in ¼ turn increments both with the new and original settings. I've changed the plug and pulled the reed block to make sure none of the reeds are cracked or broken.

The carb is supposed to come with float levels set but I checked and they are at 16mm which is correct per Keihin.

The new settings make the bike run better, but still the engine dies on long descents and will not kick start hot or cold.

I have an FMF Gold Series pipe, FMF spark arrestor, VForce reed block with carbon reeds and run 50/50 race gas and premium pump mixed 40:1 with Motul 800 2T. There seems to be plenty of compression, but I bought the bike last year used and have not replaced the top end after about 10 or 15 rides.

Any Ideas how to get this running correctly? I sold my trusty 2000 CR to get the most current green sticker model and now I'm beginning to regret my decision. Oh, I mostly ride at Carnegie since it's close to my house.

Thanks in advance,

Rich

 

[Farmer John]

The case reed CR250's put the carb at a steeper angle than the piston port CR's.
I lowered my float level a little bit. Solved the decent stalling.

 

[gpconcepts]

Hi John,

Thank you for the reply. When you say lower I assume you mean so the float bowl can fill more. How much did you lower them? Thanks again.

Rich

 

[Farmer John]

Hi John,

Thank you for the reply. When you say lower I assume you mean so the float bowl can fill more. How much did you lower them? Thanks again.

Rich

You assumption would be wrong.
Lower, as in less fuel in the float bowl. When doing steep decents gas is running out the main jet & flooding the cylinder.
As far as how much I did a trail side tweek and it worked. never bothered to measure it.

 

[2strokeYardSale]

IIRC, the Keihin on my 2002 CR250 used a 175 main with a 45 pilot and was carbureted perfectly. Perhaps yours has a slide of a wonky size. I'm not sure what it's supposed to be, I think a #7? BTW, what needle?

Got a good, fresh, clean plug in it?

 

[elemetal]

It sounds like you're pretty rich in the idle circuit: too big a pilot; too high of a float setting; dirty air filter. To confirm, with the bike warmed up and probably while riding try to turn the choke ON, if it kills the motor immediately it's a good sign you're rich.

Make sure you're cable has enough slack to ensure your slide is completely down.

I typically get the bike to idle (high or poorly, whatever I can get) by using the idle speed screw (not the AS screw) then try adjusting with the AS to get the idle lower. If you're over 2.5 turns out you need a smaller pilot, if less than 1.5 you need a bigger one.

Slide is important but more about transition than position, needle root diameter can effect idle and definitely off-idle reponse. Since your running numbers very close to 2t yardsale (that were good) I'd look to for some other issue (clogged pilot causing overly lean; clogged fuel filter or clogged vent line from carb).

 

[gpconcepts]

The carb is brand new but I suppose that doesn't mean nothing is clogged. I am unsure of the slide number or needle number but I will pull it and post tonight. Thanks again all for the help. I'll keep the post updated with my progress.