Late model vacuum ports

[jocko463]

Cliff's book recommends finding a q-jet of a post 1976 vintage. These carbs, for the most part, are early smog carbs and are loaded with all sorts of vacuum fittings. Is there any source out there to indicate what these vacuum fittings are for or what type of vacuum they provide?

[omaha]

the only ports that you would have to worry about would be the egr and the ported source for the vacuum adv. you can tell where these are by careful inspection (usually the adance port is on the drivers side on the main body, on the front down low). you can blow air theough the fitting and feel where it exits in the throttle bore to determine which one does what.  btw egr and vacuum adv each have their advantages. both help fuel mileage

[jocko463]

Thanks for the reply....Since the carb is going on a '67 Pontiac 326 I don't need to worry about EGR. There is a threaded rear tap for power brakes and a separate tap for the distributor advance (manifold vacuum). Across the front of the carb there are five vacuum taps; one large mainfold vacuum port and four others I can't readily trace. 

[omaha]

Its best to use the ported source for the distributor, its the one that has no vacuum at idle but kicks on just when you hit the gas pedal.  as long as you have all your needs covered for vacuum, you can plug the others. Pipe plugs are one option, or, if you dont mind the look, just use the vacuum caps over the nipples. btw, the one coming out of the front of the carb on top is a nipple for venting the carb to a charcoal canister not a vacuum line (not all have them). Sometimes having a source of vacuum can be used as a tuning tool for hooking up a vacuum gauge.

[Cliff Ruggles]

+1

The distributor port is in the main casting just to the right of the fuel inlet as viewed from the front.

The other front ports in the baseplate are for EGR, and late "timed" ported vacuum, except for the large PCV fitting.  If there is an additional port just above the fuel inlet, it is also full manifold vacuum, as is the one to the choke pull-off......Cliff

[jocko463]

Thanks guys. I'll probably just figure out what I need (power brake source off the back of the base plate and distributor vacuum from one of the ported taps. The others I'll just cap over; I can live with the look. And yes I do hook up a vacuum gauge (along with the Tach/Dwell) whenever I'm checking out the engine or making idle mixture adjustments.