Plugging Timed vacuum advance hose

Lots of discussion here.

The reason you pull and plug the ported vacuum line is when you’re setting your timing you set the base, then you’ll want to rev it to check your mechanical advance operation. If the vacuum advance is hooked up it’ll advance when you open the throttle covering up the mechanical operation.

Then, when you’re happy with the mechanical side, you can temporarily hook the vacuum canister to manifold vacuum and check it’s operation and amount of advance while it’s idling. Then reconnect to ported vacuum and drive happy.