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I normally post in the C1-C2 section, but these questions have to do with the Quadrajet carb, so thought it would be better here.
Everything regarding the quad says I should connect the vacuum advance to carb ported vacuum and this was the way it was on my stock '69 350 SB. But everyone in the C1 forum says this is bad, it should be connected to full vacuum. I've done both and, frankly, couldn't tell the difference. Which way should it be? Because this was a smog carb, most of the ports are now plugged.
Also, when I got the car, the port on the passenger side of the carb was connected to full manifold vacuum, see pic. That doesn't make sense to me. Vacuum connected to vacuum?? What is normally connected to this port?
Hi 59,
The vacuum advance port hose on the distributor would normally be connected directly to the carburetor.
There's typically a long piece of hose, a piece of steel 'tube', and then a short piece of hose.
Dr. R sells the hoses and tube.
Regards,
Alan
Hi 59,
The vacuum advance port hose on the distributor would normally be connected directly to the carburetor.
There's typically a long piece of hose, a piece of steel 'tube', and then a short piece of hose.
Dr. R sells the hoses and tube.
Regards,
Alan
This is a 71 but your 69 was similar.
Thanks for replying, Alan. Yes, I have this tube and removed it because several people said it's better to go full vacuum. I'm trying to find out if that is true on a Quadrajet.
Also, your pic doesn't appear to have that vacuum port on the right side, so I assume it's not needed.
Hi 59,
There seems to be various opinions about vacuum advance.
Since I strive to have things set up as they originally were I didn't consider any possible options.
The 71 sb version of the q-jet doesn't have the 'pipe' on the right side.
Again, not sure about the 69 sb q-jet's configuration.
Regards,
Alan
Running off full vacuum with be better driveabilty wise, you'll get a smoother idle, slightly better off idle throttle response and the engine will run cooler while its idling. I've done some experimenting with my 68 and the smog machine at work and found that running off ported vacuum will greatly reduce hydrocarbon emissions on idle. If the car has to be smogged and there is a idle emissions test ported is the way to go, other than that I'd go full vacuum.
Running off full vacuum with be better driveabilty wise, you'll get a smoother idle, slightly better off idle throttle response and the engine will run cooler while its idling. I've done some experimenting with my 68 and the smog machine at work and found that running off ported vacuum will greatly reduce hydrocarbon emissions on idle. If the car has to be smogged and there is a idle emissions test ported is the way to go, other than that I'd go full vacuum.
Advance can hooked to ported vacuum was an EPA 'thing'. Ported vacuum at idle has ZERO vacuum. Thus, the engine ran retarded at idle and burned hotter to eat up more hydrocarbons. But, it also used more fuel; and running hotter at idle wouldn't do anything good for your engine.
Idle will be smoother, engine run cooler, and fuel mileage better with advance can connected to manifold vacuum.
Advance can hooked to ported vacuum was an EPA 'thing'. Ported vacuum at idle has ZERO vacuum. Thus, the engine ran retarded at idle and burned hotter to eat up more hydrocarbons. But, it also used more fuel; and running hotter at idle wouldn't do anything good for your engine.
Idle will be smoother, engine run cooler, and fuel mileage better with advance can connected to manifold vacuum.
Great, just the answer I was looking for. Appreciate the response.
07-12-2015, 06:58 AM
Quadrajet Ports
