250MC has gone LEAN!

[GasMCAndy]

I am figuring crankcase leak? Without substantial weather or altitude changes the 2003 250MC has REALLY gone lean. Progressively loosing power on Top End. Bogging on the main with slight pinging at about 3/4 throttle. Low throttle seems great on power...

35 hours on new top end
PWK 38 RB modified carb. Cleaned thoroughly-no change. Floats good at 16mm. 45Pilot/188 main as I've been riding this winter. CEK moved today from usual 4th to 5th to get ANY color on new plug. Sea Level/50F southeastern Washington State.
Good fuel filter
15 rides on new Boysen Reeds and gaskets. Properly torqued.
I sprayed Carb cleaner around the cylinder base, reeds, case seams at idle- no idle change.

Thanks for your replies! -Andy

 

[roostafish]

Good call on the carb cleaner test. It still may not react the way you want it too, so a good visual inspection of the rubber boot on the output of the carburetor is in order. A likely suspect is the left, or ignition side crank seal.

I have had the crank seal on the ignition side fail (on a KTM) and give similar symptoms. If you pull the ignition cover off and it's full of a bunch of crud and rust, it's a sure bet that seal is junk. The good thing is if you haven't damaged the bearings, you can just pull the flywheel and replace the seal with the bike on the stand.

 

[PEB]

I have had more than one of those carb boots crack. Mine gets changed yearly now.

 

[GasMCAndy]

OK- looks like a simple cover removal and inspection is in order. I did inspect and carefully align and clamp the double clamped carb bootie- it's in good shape.

If no sign of crud in the seal area I will probably still replace. Also new top end rings, base gaskets, exhaust valve clean-up, ect. Won't be able to put a load on it for a little bit to check power loss area but it will allow me to measure fit/ring gap. I did see dark carbon between the rings about 15 ride hours back with the exhaust off. Was told this is normal.

Thanks and please add more comments still if you wish.

 

[GasMCAndy]

Anybody know how to remove a duplicate post? I've looks everywhere and webmaster is not accepting emails.

 

[gasgasman]

Anybody know how to remove a duplicate post? I've looks everywhere and webmaster is not accepting emails.

Other post deleted.