i bought a new vacuum advance because the old ones diaphram was old and leaked, but it only had one.. i went and bought a new one that works well, but it has another smaller brass port on the top side. what should i do? just plug it or put another vacuum line from the carb to it?
If we had some pic's we could be sure of what you have. But if it has a tube on both sides of the diapham I wouldn't plug one as they are both sealed areas. If you plug one you will be causing a vacuum in the other and you will never get the right advance. Dual ports are for retarding and advancing the spark depending on driving contions, if you retard the spark at idle your engine should run cooler. But pic's would help Rick
If the second port is on the side towards the dist it is the 'retard' port. You don't need to connect it to anything. But don't plug it as it restricts the vaccum side ot the diaphragm from moving freely. RS Oops guess I just duplicated what 'rickm' said.
My GTO had a similar set up. It had a ported vacuum switch that blocked the retard function until it warmed up.
