Does anyone know what vacuum line goes where, on a dual vacuum line distributor...for a 1967 firebird 400 California/smog engine with Auto. trans. A/C They say that this is a very rare distributor

4th illustration down:

Firebird Engine Vacuum Diagrams

Thank you very much for the pics.. No wonder the bird runs bad I had all the vacuun lines wrong.. Jerry

Im interested to know if those dual diaphram distributors are really that rare...


'cause I have one sitting in a box in the attic.

Do you still have your smog equipment, unique carb and unique air cleaner?

I also have the smog motor and Im trying to re invent the wheel. No Im trying to restore it. I also have a dual port distributor. Which I think you mean the normal port coming oiut not the vac advance and then another coming out the opposite back side lower of vac advance? Where do these vac lines go? Any help would be great. Thank you joseph67

I have a '68, which is quite different than the '67s. However, these two pages from the Parts book Diagrams may (or may not) help.

I have never seen one of those on a Pontiac. But I think the idea was to retard the timing on deceleration, right? Because otherwise closed throttle deceleration would advance the timing. Oddly, I knew a guy building a car from scratch in his garage. He was using an old 80's Toyota 4 cylinder engine and it had a dual port distributor. I think some Fords used it too.

The '68 had a vacuum retard as part of the emissions changes for that year. It connects to one of the five ports on the TVS. A tech bulletin (68-T-2) removed it on many V8's. To date, after a lot of studying it, I still don't know if 400s were meant to be included on the bulletin or not but it was removed by Mr. Goodwrench on my '68 400HO way back in the early '70s. In '69 the TVS lost two ports.

Edit: Yes, according to the '68 Diagnosis manual, it was said to be there to reduce timing on idle and "coast down" to reduce emissions.

(I have been thinking of adding "dummy" striped hoses back to the removed TVS hoses for the original appearance, thinking the 400s were not supposed to be part of the bulletin.)

Looking at those parts diagrams, it appears to be something associated with the '67 California AIR equipped cars which joseph67 mentions.

They really struggled with emissions back then. I had a 1967 400 HO parts car. I can remember the drilled ports in the 670 heads for the AIR tubes. Mine were plugged. Then I remember reading that Pontiac was able to eliminate the AIR system in 1968 by going to open chamber heads VS the closed chamber '67 heads. I did not see AIR again until the 1980 301 engines. My 1972 Catalina 400 had the TCS switch. It only allowed vacuum advance in high gear. I quickly eliminated that stupid idea.