Help!!!

Sounds lean. And with no jetting cahnges, I'd look for an air leak.

MJ 410
27.5 pilot jet (stock is 30)
needle 6BEY30-74 3rd clip
AS 2 turns out ( I then turned it to 1 1/2)

my jetting is exactly the same on a 03 cr250
fatty
vforce
except the needle is a 6BHY38-74 3rd clip i believe your needle is stocker for an 02
i dont know if this helps any other than that i would run the motor and spray some starting fluid around and youll know if theres an air leak

hard to picture but if im getting what youre saying i would think that the reeds actually protrude into your case past the gasket

Air leak. The left side crank seal is suspect and cheap/easy to replace otherwise it's probably leaking else where. Either way If you want to be sure you can build your own leak tester to see if your motor is leaking; a lot cheaper than the alternative.


Leak Tester:

http://www.dirtrider.net/forums3/showthread.php?t=87952


Crank Seal Replacement:

When you pull in the clutch cable air will leak down the cable into the ignition cavity in the case. Try pulling in the clutch or wriggling the clutch cable where it enters the case with the bike running on the stand. The R's should go up if you can get air around the cable. Sure sign the seal is leaking.

If you have a flywheel puller then you're set. Start by removing the four 8mm bolts that hold the ignition cover on and remove the cover. Hopefully you have an impact gun at your disposal. Use it to remove the 17mm nut that holds the flywheel on. After you've removed the nut (and the washer behind it) you can thread your flywheel puller on. Pop the flywheel off.

Next remove the two 10mm bolts that hold the stator on and gently pull the stator off. When removing your stator you'll notice a mark on the bottom and one on the cases. These are timing marks and need to be lined up when reinstalling the stator. Don't worry though, unless you've notched the bottom mounting hole and played with the timing prior to this then you should have nothing to worry about. You can either set the stator off to the side or disconnect it and remove it, what ever you want to do.

Now you can see the seal. Grab yourself a smallish (1-1/2" or so) wood screw and screw it into the seal. You can use more than one if you'd like (another on the opposite side work well) just make sure you work slowly when getting the screw to grab. After this I heated the case a little with the propane torch and then grabbed the screws with a pair of pliers and pulled the old seal out.

I installed the new seal with a dab of grease and a 7/8" (I think) deep well socket, taking care to make sure that it went in straight and to the proper depth outlined in your manual. After the seal is in the it's just a matter of putting everything back together.

pro2k said:

...and didn't start doing this unitl I pulled the valve and replaced the gaskets there... Do you still suspect an air leak??

Click to expand...

IMHO, most likely...only one way to know for sure though. I only mentioned the crank seal as a possible suspect given what you had said. I leak test my motors after every rebuild to be 100% sure now, there's been times where I was confident it was tight only to have the leak test tell me otherwise (and save me headaches).

pro2k said:

Where can you get the little bulb to pump up the pressure? (did you mention that?)

Click to expand...

No, I used a bicycle pump. You should be able to get the bulb pump at a medical supply store or something though. Good luck.

Anything that will read low air pressure fairly accurately that you can get to seal and will not leak.

The gauge I used is for testing gas/plumbing lines, just a basic pressure gauge with a 3/4" (I think) threaded (female) end. You might try calling around to local places that might carry those types of supplies and see what you come up with. If not use what you have at your disposal. Good luck. :cool:

Does it matter whether or not the engine sees vacuum or pressure? On the link you provided to Eric's book, he said that you pump it down to 5 psi vacuum, not 5 psi of pressure. I mean, if you have a leak, you have a leak, but should you really test it with vacuum instead of pressure?

The Motion Pro unit that retails for well over $200 tests pressure not vacuum. I've thought about making a leak tester part II that would use a Mity Vac to create a vacuum for those interested in exploring that route, even with the Mity vac supplies could be had for way less than the MP unit (I guestimated the $50ish range).

I understand that as the piston is on the upstroke it creates vacuum and would suck air if leaky seals were present, but wouldn't those same seals leak as the piston was on it's desent causing the crank case to see pressure? (before the transfers are uncovered...) IMHO I think the pressure test would be more acceptable than just guessing in any case.

I agree, I am sure some test is better than none and I honestly have no clue if there actually would be a difference in how the seals etc. would act. Thats why I asked....

Pro,

Did you solve the problem. I have a 98 cr250 that does the same exact thing. I've tried the air/idle screw which helped a little but everyone tells me it has to be the carb. I've only had the bike for a month and the previous owner had the top end redone a few months before I bought it which leads me to beleive there might be some possible air leak created when the top was rebuilt. Argghh. let me know if you solve your problem.