Help!!!

[pro2k]

Ok I have a 2003 CR250 that I JUST rebuilt and broke in last weekend. I didn't change the jetting at all and everything is the same as it was before the rebuild. When I broke it in everything seemed fine but yesterday I took it out for some gnarly woods riding and it would have some issues down low on the throttle. When I was using the throttle and the bike was under a load it would run fine but when I let off the gas and was coasting in gear, clutch in, it would have a slight knocking sound and the engine would 'hang on' to a high idle. If I revved it up it would return to a normal idle. When I went in for a pit stop I turned in the air screw about 1/2 turn and that seemed to lower the idle and help slightly with the knocking but then I noticed when I was coasting in gear on flat asphalt road that it would surge, return to a coast, and then surge again. Everyone with me said the thing was smoking plenty when I was riding. Here is my jetting for about 900 feet and temp was 70.

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)

What the heck is the problem?? Funny thing is these are the settings I used before the rebuild and it was all good. I did change the PJ from a 30 to a 27.5 awhile back and haven't been in the woods with it. Been on MX tracks since then where you don't see much of that circuit. Could there be an air leak somwhere? HELP!!!!!

 

[tony91]

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

 

[ellandoh]

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

 

[pro2k]

After I broke it in I took the reed valve off and checked the reeds and replaced the gaskets when I put it back on. One thing I noticed is that the cut-out in the new gasket was slightly smaller on one side and actually covered the hole in the reed valve by a few mm. (carb side) Does that make sense? What I'm saying is the gasket material overlapped the cutout for the intake on the valve. I'm sure that it would mess with the fuel/air flow somehow but would it cause these lean symptoms?

 

[ellandoh]

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

 

[pro2k]

It's the other side of the valve closest to the carb.(the intake side of the valve) The air/fuel mixture flows from the carb through the boot, and into an oval cutout on the valve and then through the reeds. The gasket overlaps the oval cutout slightly.

 

[Faded]

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]

I tried squirting starting fluid around the valve and around the cylinder gaskets and it didn't do anything so I don't think there's any leak around those gaskets. The motor doesn't start surging and acting lean until it is hot from woods riding. I didn't really notice it when I was on the track. I was thinking of putting the 30PJ back in.

 

[pro2k]

faded, when I was coasting down the street in gear and it was surging the clutch was out. It was running perfectly before I rebuilt the top-end so I would think it was something I did wrong there and not the crank seal you mentioned. It also seemed to run fine when I broke in the motor and didn't start doing this unitl I pulled the valve and replaced the gaskets there. Then again, I didn't really ride it hard until this past weekend when I was really getting on it and heating up the motor. Do you still suspect an air leak?? (I will also try to wiggle the clutch cable and see if the motor speeds up, like you suggested) Thanks for the help!

 

[pro2k]

I went out and idled the engine and squirted soapy water around all the seams and found no bubbles anywhere. (but I guess if it where sucking air in you wouldn't see bubbles anyway?) I also pulled in the clutch a bunch of times and wiggled the cable by the ignition cover and it never raised rpms even slightly. It is very rich at the bottom end with the AS at 1 1/2 turns. it puffed plenty of smoke and blubbered. Is it possible the engine would load up with fuel and cause a surge, burn it off, and then go back to idle?

Man, that muddy woods riding is brutal on my bike. I noticed that BOTH of my forks are leaking now. The place we went was an old abandoned strip mine and the mud is thick clay like crap and sticks to your bike like glue. Wrecked havoc on my fork seals and took like an hour to clean the bike off!

 

[Faded]

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

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]

Ok. I think I will go buy the stuff to make that DIY leak down tester. Sounds like a cheap way to go...thanks for the info. Where can you get the little bulb to pump up the pressure? (did you mention that?)

 

[Faded]

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

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.

 

[pro2k]

Faded, thanks for the help. Today I went to HOme Depot for the gas pressure gauge and they had nothing like it. I gave them the part# and sku from your other thread and they came up with nothing! What else can I use? Would a guage off and old foot operated bicylce pump work?

 

[Faded]

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:

 

[Dragmeistr]

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?

 

[Faded]

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.

 

[Dragmeistr]

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....

 

[pro2k]

Can you overtighten the airbox to carb and the carb to case boots? I mean if you overtighten will the seal be deformed and air leaks occur?? Still trying to figure out my airleak problem. I took the reed valve cage out today and the gasket between the carb and valve was completely soaked with fuel. I know I torqued the bolts to specs (7lbs) so I am a little puzzled by this. I replaced the gasket with a new one and torqued the bolts to about 9lbs this time. Curious to see if this helps.......

 

[Butane]

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.

 

[pro2k]

Butane, I built the diy leakdown tester and pumped it up to 8psi and the pressure fell rapidly. I made up some soapy water and sprayed it around the cylinder gasket and reed cage area and then pumped up the pressure. It immediately began to fizz and bubble around the cylinder gasket. Well, I took the cylinder off applied a little gasket sealer at the problem area, put it all back together, and pumped it up to 8psi. No leaks and the pressure didn't drop off at all after a couple minutes. I haven't been able to take it out to the track yet but I'm almost 100% sure that leak was the problem. If you are having the same problems and the top-end was recently rebuilt I would suspect an airleak. Your bike is also a little older than mine so it could quite possibly be that crank seal Faded was talking about. You can squirt some baby powder around the gaskets and run the engine and the powder will highlite the area (or so I have read). But for less than $30 you can make the leakdown tester and know for sure if you have an airleak. Good luck and let us know what you find!