Jets for the CRM250 carb - Keihin PE31*** should be available from any MX dealer as all Keihin PE carbs (and some others) use the same jets.

Skidmark kindly put togther this list of relevent topics.

viewtopic.php?f=6&t=4316

viewtopic.php?f=6&t=3836

viewtopic.php?f=6&t=2993


eddie666 has found a site relevant to setting up carbs -

http://twostrokemotocross.com/2009/12/c ... nd-tuning/


This site has very good directions for setting up a 2 stroke carb. (The numbers are for a KDX220 but the theory is exactly the same and this is the closest engine to the CRM performance wise).

http://www.justkdx.dirtrider.net/printcarbtuning.html

Further -

http://www.angelfire.com/zine2/boostaje ... uning.html

I used Keihin PWK 33mm on my 2 Mk1s. They massively improved throttle response. The only change I had to make was to cut ~10mm off the outer cable going to the oil pump to be able to get the carb and pump in sync and align the pointer on the pump so that it went past the mark on the pulley by 1mm to be sure there was enough oil at full throttle. I tried different jetting but in the end settled on what was basically the same as I would have used with the original carb.

In Japan the 35mm PWK is quite popular but you have to go premix because the difference in the carb pull distance and the oil pump is too great.

Both give much improvement in throttle response but the 33mm keeps the low/mid whilst the 35mm sacrifices some of this for a small amount of top end.

FallenMiketheBike has written the following about tubes on the carb -

The clear/ opaque jobbies are the carb breathers and overflows.
5mm plastic pipe from motor factors shop, or even better silicone pipe.
Link out the breathers above the carb using again from the motorist shop a 3 way windscreen washer fitting.
Then take the pipe to either the headstock or the air box.
The overflow pipe, drains down to near the linkage assembly.
Either wrap the end in some sponge, or cut to 45 degs, to help stop crud blocking the end up.
The water hoses, whose purpose is to stop carb icing, which is a condition were unlikely to get in this country can be removed altogether, [ which I have done] obviously you need to seal the ends where these formerly attached.
This is the last time I'm writing this flow chart, I'm sure I've written it on at least 4 occasions before.
Mike