I've been having some problems lately with my 68 Mustang idling rough (which I think is just idle mixture adjustment) and not the best power/acceleration but I was wondering which port is better to connect the vacuum advance to - the timed/ported one or manifold. My C6 also uses a vacuum modulator so I currently have it connected to the manifold vacuum and the vacuum advance connected to the timed one. But I read recently that only emission controlled vehicles (which mine is not) are supposed to connect the vacuum advance to the timed port. However I don't know that my transmission would work properly if connected to the timed port. Any advice anyone has would be much appreciated. Thanks!

 

The transmission must be connected to full intake vacuum.

The vacuum advance, by default, is hooked up to ported vacuum. That said, you can tune the car to run with it hooked up to manifold vacuum. Takes a little tweaking of the advance curve, but it can help even out rough idle caused by valve overlap.