Can't find my leak anywhere!

[SoFlo]

I'm doing a leak down test on a 1996 RM250.

I has a very hard time holding above 5 psi. It'll hang around 3, and drop slowly from there. Around 5 it drops fast.

I have a freeze plug in the exaust, my tester in the intake, the head is on, everything is on, besides the coolant hoses, but those wouldn't technically need to be on for this test, as I should have a seal there.
I had a leak on the right powervalve plate thing, fixed that, and I had one on the base gasket, fixed that, but I'm still loosing pressure fast. As far as I can see with my soapy water, the intake manifold, the tester, the freeze plug, the powervalve covers, the powervalve vent hose, the base and head gaskets, the spark plug, are all holding perfect with no bubbles forming.

When I take my oil fill cap off, I loose pressure from there, but that's because it goes through the exaust, down the linkage thing on the powervalve into the clutch area. My right hand seal is new and the bike hasn't smoked at all.

My left side seal is also new, and there is no oil spewing around in there, everything is bone dry.

Nonetheless, I am also not loosing pressure out of the clutch cover or the flywheel cover, so even if those seals were leaking, it would eventually pressurize the whole side and not leak. I can just sit there and pump and it just keeps loosing pressure non stop.

Any ideas where I can find some leaks?

 

[sick 96 250]

are you saying your exhaust is still on the bike and you have it plugged? If so thats prob your problem, pull the exhaust and plug up the exhaust hole on the head. WHy do you think you have a leak somewhere anyway?

Also make sure the plugs are really sealed up well. Could you be losing some pressure where your pump is hooked into the intake plug, assuming that is where you are taking the reading from?

 

[airmanloco]

No bubbles coming up out of the coolant at top of radiator, just in case you had a bad seal that was allowing it to leak into there, oh you said you had the hoses off didn't you so I guess you wouldn't be able to check this. Otherwise I would second what the guy above me said with having the pipe off and connecting right to the exhuast port. One other thing, my modified YZ250 has the powervalve cavity vented to the outside air (not sure why they did that, bought it that way and they were pro racers), make sure yours isn't. Good luck.

 

[SoFlo]

My exaust pipe has been off, I'll keep looking.

 

[photomd]

If you can find an old stethoscope, pull the end off you put on the patient and start tracing all the gasket areas. You'll hear the air leak if that's the source. A length of fuel line held to one ear and an ear plug in the other will also work.