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Smegol

Sucking Sound Near TDC

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Recently my 400 has been down on compression, and it is getting really hard to find the "right" spot with the decomp lever. I'm getting rather tired of it kicking back and trying to break my ankle. It even put a hole in my shoe the other day :thumbsup::devil:. Anyway, I decided to check the valves and all of them are in spec except for the far right intake (right being the clutch side), which is right at the limit of being in spec or not (.14 - .15mm). But one thing that caught my attnetion is I can hear a sucking/blowing sound coming from around the valves near TDC and was wondering if this is normal or not.

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You might be hearing the piston blow-by that is happening in the crank case, which is connected to the valve area by the opening that the cam chain runs through. If you have leaky valves then you would be able to hear them through the exhaust pipe and/or intake side. Put your ear at the end of the exhaust (disconnect the spark plug wire!) and have someone slowly kick it over and listen for the hissing. Do the same but put your ear on the carb side with the throttle open. If you hear any hissing then those valves are leaking.

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