[Andrew140]

Hi everyone I am new to CRF's only. I bought a 2009 CRF250r and am having problems with the infamous bog. Anyone have any suggestions on jetting? I don't really know where to start. Also, I have read some threads on the o-ring accelerator pump mod and am wondering if that will work on this bike. Thanks!

[Andrew140]

I forgot to mention the bike is completely stock and I am at about 1000ft. above sea level.

[jjrace]

HEre is my C&P from an identical thread:


Ok you have a few things going on here.

First ditch the AP cover and go back to stock or one like the R&D or Merge that has an adjustable leak jet.

After that it is most likely hard starting for 1 or 2 reasons. 1st you need to remove the hot start plunger from the carb, grease the plunger lightly and then reinstall. AFter that adjust so there is freeplay at the lever. If that is stuck open it causes a lean condition. 2nd your pilot jet is most likely plugged up. It also could be the wrong size. Start by cleaning it out, then looking through it to make sure it is clean. Compressed air and some carb cleaner works great.

Put the carb back together and see if that helps.

If not, next step in the crf250s is to lower the float height. They are to high with that larger carb from 06-09 and when you land the excess fuel sloshes out into the cylinder. So lower the float level by about .5mm, just so that only 3/4 of the bowl fills with fuel.
Next you are going to want to modify the AP circuit in carb.

If you still have problems, be sure to try the simple things like different clips on the needle. If that does not help, then go back to the stock clip. Also they are jetted lean, so going up 1 size on the pilot usually is very helpful and keeps it from poping on decel. Leave the main stock (adjust for altitude here).

Now if nothing else so far has helped, time to modify the AP circuit. 2 ways to do it - put some money into it with getting an adjustable leak jet (mentioned earlier) or modifying the AP linkage and trying a few different size leak jets. Here is a link for you to read up on:

http://www.squadpage.com/pandora/Profes ... %20Mod.pdf

On my 450 I ended up with a #90 leak jet.

Hopefully that helps you out!