Charcoal canister behavior?

[Earendil]

I recently did a vacuum smoke test of two M20 engines. On one M20 engine we got a little bit of smoke coming out of the base of the charcoal canister. On the other M20 there was absolutely nothing.

The question is which behavior would be the proper behavior for the charcoal canister when doing a smoke test? Thanks!

[jlevie]

Except when commanded by the DME the valve between the charcoal canister and the throttle body should be closed. It sounds like the valve on that car is bad as there should be no way for the smoke to reach the canister with the engine not running.

[nando]

yep, the valve should be closed when not powered, and only opens during part throttle cruise.