Motobecane Decomp valve - compression loss maybe?

So I think I have an air leak and I'm almost sure the decompression valve is part of the problem. I've taken the exhaust off, and when I turn the variator, I can hear air escaping somewhere. When I put my finger in the exhaust hole, and cover the little hole that leads to the decomp valve, I can feel the compression increase, and air trying to escape around my finger, even when I'm not pushing the valve down.

Is this supposed to happen? I'm assuming everything should be airtight. How hard should it be to move the piston without pushing the decomp valve down?

Re: Motobecane Decomp valve - compression loss maybe?

scott middleton /

disassemble and get some valve lapping compound at your local auto parts store, then lap that sucker for a better fit. (edited)

Re: Motobecane Decomp valve - compression loss maybe?

Lapping the valve didn't seem to change anything. Air still comes out the vent by the exhaust. Any other ideas? Do I need a new valve?

Re: Motobecane Decomp valve - compression loss maybe?

simon thokaar /

replace it with a high comp head, or fill it up the hole with jb weld.. decomps are for suckers!

Re: Motobecane Decomp valve - compression loss maybe?

Out of curiosity, how hard is it supposed to be to turn over the engine without using the valve?

Re: Motobecane Decomp valve - compression loss maybe?

scott middleton /

if it's a 50cc, it's not bad. assuming the the ped is in good running order. I have an Airsal 50cc AV10 with no decomp, no probs.

Re: Motobecane Decomp valve - compression loss maybe?

Lapped it better, seemed to fix the problem. Used a drill to spin it real fast and grind it better.

Condenser is what was making it not run, but at least now I have good compression too!

Re: Motobecane Decomp valve - compression loss maybe?

scott middleton /

right on!

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