The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

68gmsee · 09-15-2017, 10:06 PM

Sounds like you had the vacuum advance on the manifold vacuum and moved it to ported vacuum. A lot of people like the manifold vacuum over the ported vacuum but it depends on the carb adjustments and engine settings which is better for a particular motor. Personally, I've used both on mine and really never noticed a difference once the idle rpm was adjusted. right now I'm using manifold on my GMC and it likes it.

In your case, I don't suspect it will make much difference in your gas consumption but if it seems better than I'd leave it as it is. Once the you're on the road and off idle, they operate the same.

09-15-2017, 10:06 PM	#15
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: I could use some Quadrajet Guru help Sounds like you had the vacuum advance on the manifold vacuum and moved it to ported vacuum. A lot of people like the manifold vacuum over the ported vacuum but it depends on the carb adjustments and engine settings which is better for a particular motor. Personally, I've used both on mine and really never noticed a difference once the idle rpm was adjusted. right now I'm using manifold on my GMC and it likes it. In your case, I don't suspect it will make much difference in your gas consumption but if it seems better than I'd leave it as it is. Once the you're on the road and off idle, they operate the same. __________________ 68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...