Ported v. Manifold Vacuum for distributor
 

I know this has been discussed before, but I am struggling to get my timing set. I thought I slipped the outer ring on my harmonic balancer, but that looks fine (thank you Jeff). Anyways, I am setting up my new EFI using the ported vacuum for the distributer and it just doesn't respond correct. It tells you to set the timing at 5 degrees with the vacuum disconnected. I am questioning why you would need to disconnect the ported vacuum because at idle it is effectively 0 inHg meaning it really has no impact on the advance. I checked the ported vacuum and sure enough it you rev it up, it defiantly actuates.

I looked in the shop manual, and it is silent on which vacuum source to use on non-AIR L6 cars. Interestingly, on V8 cars it says "The vacuum advance is connected directly to manifold vacuum so there is full vacuum advance at idle." So I am questioning, should I also connect to full manifold vacuum. I don't remember how much vacuum existed on my Quadrajet but I do recall the timing shifting a bit when it was disconnected. Any ideas?

Your mistake is following the initial timing indicated in the Pontiac manual. Gasoline is completely different today than in 1966. You want to be 5 to 7 degrees on top the 5 before TDC. So 10 to 12 degrees before top dead center is a good starting point. Don’t switch vacuum sources just yet. See if your EFI likes that much better.

Ok that makes me feel much better. I am 12 to 15 degrees currently and it runs infinitely better. At that timing my vacuum is good and it runs much smoother. I am still letting the EFI learn at this level before I start tweaking the accelerator pump settings.

Great to hear! You are on your way then. Good luck!

Which EFI are you using? Why did you switch.from carburetor? Do you like it? I have been intrigued by the quadrajet sniper EFI by Holley.

I went with the FITECH unit. Overall happy but I have one issue I am still working where it bogs down when I give it a throttle hit with the clutch in. All other times it runs great. I switched because I needed to rebuild my carb again. Instant starts all the time. Runs much cleaner without the obnoxious gas smell I always had. Also allowed me to put a new fuel pump in the tank.

Does the fuel pump in the tank also have a sender unit? The stock tank has one opening for the sender, the aftermarket FI tanks I've seen have two openings, one for the pump and one for the sender. Also, where did you mount the O2 sensor?

O2 sensor is approximately 6-8" after the Y-pipe. The Spectra tanks have one opening for the fuel pump and level sensor. I had an issue with the original fuel pump, the second fuel pump has been working fine.