- Thread starter
- #21
It looks like the advance port on a '78 carb would be roughly equivalent to the EGR cut port on a '77 (comparing this diagram posted by Jim C. of a '78 desmog setup with the diagram at the beginning of this thread):...The distributor functioning is pretty different...78 carbs have an EGR port, an advance port and a TP port. I don't know what an EGR cut port would do. A 78 distributor requires the 78 computer to function to factory specs. That doesn't mean you can't run it but the distributor should be recurved and you would only need a line from the advance port on the 78 carb to the vac. adv. can on the 78 distributor.
My '79-'80 dizzy has two vacuum ports, and is a dual-vacuum advance dizzy. I'm not sure which diaphragm is primary and which is secondary in this setup, but I know on some dizzies the outer diaphragm is the primary and the inner diaphragm is the secondary, which would typically be connected to the High Altitude Compensation (HAC) valve.
No that's not a fuel bowl vent. I don't remember what Jim C. called it but it has a little flapper valve in there that opens and closes with vacuum. I didn't know that it connects in the way your is - i.e. - to the vacuum surge tank which is a 77 specific smog component and not found on a 78.
I'm pretty sure I inherited my 40 with that hooked up that way. It sounds like it needs to be changed.
The different VTVs seem to bleed off or allow the build up of vacuum at different rates. The different BVSVs open at different operating temps to control when various vacuum-actuated smog stuff comes into play.
That's what I figured, thanks.
You need a 77 and a 78 emission manual to compare how all the above systems work. They will tell you when each system is operational by temp, etc.
Working on getting that together now, thanks.
At this point, with the new information I've learned so far, I'm inclined to put the smog stuff back on. Unfortunately I've taken a liking to my fully electronic ignition system (no points adjusting), so it would be nice if I could make my '79-'80 dizzy and '78 carb work with the '77 emissions system. It would be really cool if all that took was to take the advance can from the dizzy and plug it into the advance port on the carb, then all my vacuum ports would be hooked up to something
Last edited: