1997 CR250 Idle problem

[jammin-johnny]

Hello everyone,
My 97 honda has a fluctuating idle. It surges when I am slowing down and when the bike idles it revs up and down. I think its sucking air, but I don't have pressure testing equipment. I checked the carb insulator and it is clean and tight. Any Ideas on how to identify an air leak somewhere on the engine? Also If it might me a crank seal, which side causes the engine to run lean and which side causes it to run rich?
Thanks.

 

[motofreak24]

to check for air leaks put soapy water in a squirt bottle and spray the motor. if you start seeing bubbles you have found the leak.

 

[kuritaro9]

also,i would suspect a leaky crank seal under the flywheel.pretty easy to replace.my bike did the same thing,and thats what was wrong. :cool:

 

[kuritaro9]

i would think the right side would make it rich,due to sucking the oil in and the left would make it lean(no oil to suck) :cool:

 

[nickyd]

everybody's right!!!! confirm you don't have a leak externally via a soapy water solution and then go after that crank seal! (the magneto side)

 

[nickyd]

also,i would suspect a leaky crank seal under the flywheel.pretty easy to replace.my bike did the same thing,and thats what was wrong. :cool:

were you able to replace it w/out splitting cases?

 

[Toothmech]

You don't have to split the cases. Just pull the flywheel, and stator plate. Drill a small 1/8" hole into the existing seal on opposite sides of the crank output shaft(don't go too far and damage the aluminum case). Then thread in screws(sheetmetal) that binds tightly in the holes you drilled. Grab the screws with pliers and yank, the seal should pop right out. Clean the sealing surface and tap the new one in with a rubber mallet/ deadblow hammer and a piece of PVC pipe that matches the outer diameter of the seal. Be sure not to hammer the seal too far in. Some bikes have a flange that the seal seats against, others don't, so I recommend measuring how far the seal was set into the case prior to removal and relplacing it to that depth. Reassmble and pat yourself on the back for fixing the problem. Hope this helps.

 

[nickyd]

Thanks Toothmech - I've done that for the tranny seal (output shaft) tons of times....I've always seem to have gotten to bikes with fried top ends due to the leaky seal and have been forced to split the cases due to this issue...Just was wondering if someone out there had done the seal pull with the sheet metal screw as you mentioned - now I know and I'm all over it next time I suspect that seal is beat.

 

[darringer]

On the '97, when replacing the seal behind the flywheel, it is possible to tap the seal in too far and block off the oil passage for the main bearing. Just install it so that it's flush with the case flange. That way the passage is not blocked. Too deep, and you'll be splitting the cases.