97 CR250 Air Leaks Driving Me Crazy

[mylesc]

I've been chasing my tail trying to track down an air leak for a while now on my 97 CR250. My bike would surge and knock at low throttle openings and closed throttle deceleration.

I tried to richen up the pilot circuit and went all the way up to a 65 pilot. The low, 1/8, throttle opening knocking went away but the bike was running way way rich. The closed throttle decelaration surge was still there.

I tried richer needles and clip positions but couldn't get rid of the surging under deceleration. I built the leakdown tester found here:

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

and I was losing about 1.5 psi per minute.

The cylinder base,head, and intake showed no leaks using windex to show any air bubbles. My left side crank seal was leaking so I replaced that. I did another leakdown test and it was a little better but I was still losing 1.25 psi per minute.

I pressurized the tester again and stuck the tranny breather hose in some soapy water and it immediately started bubbling. I 'm not losing any tranny oil so I didn't think that my right side crank seal was bad.

I removed the right crank case cover and sprayed some windex on the right crank seal and no bubbles. I coud hear the leak and tracked it down to the pinion shaft that's driven off the crank to control the exhaust valve.

So air is traveling from the top end exhaust valve drive shaft down to the tranny. The shafts look to be in good shape with some looseness in the bushings. I ordered new bushings and will compare their tolerances to the old ones.

While the RH crankcase cover is off I'll go ahead and replace the right crank seal since it's cheap and easy to replace.

Has any one else ever experienced this weird source of an air leak before? Is there any other possible source for an air leak that I haven't checked for yet?

I'm waiting for parts right now so it will be a week before I can get it back together for another leak down test.

 

[Faded]

mylesc,

Sorry to hear about all the bad luck. Hopefully this will cure your problems. I'll be rebuilding a '99 soon and will be leak testing it before running it in. Just wanted to say thanks for the tip, I'm just sorry it came at your expense. Good luck! :thumb:

 

[mylesc]

Thanks for the encouraging words Faded :thumb: . I can definitely say that I've gotten my $17 worth out of that leakdown tester.

One bit of advice for you, do the leakdown test before you tear down your friends motor. If you have a leak like mine or the right crank seal, the top end needs to be off to fix it.

 

[Faded]

Good deal, looks like I'll replace the left side crank seal first (I know it's bad) and then leak test before (and after) the top end. Hopefully yours makes it bad together without a leak this time around, good luck!

 

[Mike_socal]

This an old post but I have the same exact problem on my 2001 cr250. I have an air leak traveling down the pinion shaft that controls the exhaust valve into the transmission. Where should the air be stopping? At the pinion shaft metal bushing or higher up in the exhaust valve cavity?

 

[mylesc]

Wow, this is an old thread. I've since sold my 97 and gone blue. I think it's safe to say that air should not be getting past where the bottom end pinion shaft meets the top end exhaust valve shaft.

When I replaced all of my bushings I followed the Honda shop manual recommendations about where to grease and what kind of grease to use. When all of that was done, the leak down test held tight for 5 minutes. Good luck