I noticed the "ported vacuum" source was intended for the distributor advance on the Holley instructions.
But on my assembly manual for my 1978 250cid Camaro, the vacuum advance is connected to the vacuum port on the bottom of the carb along with a tee to the THERMAC air cleaner. The ported source higher up on the Monojet goes to the EVAP canister valve. The PCV and EVAP lines are hooked to a source on the integrated manifold. If it had power brakes there is a plug on the integrated manifold below the linkage where it would connect.
I'm wondering why if the distributor vacuum advance needs a ported vacuum source, why is the stock one connected to full manifold vacuum? Is it because there is a delay valve in the vacuum line to the distributor that is controlled by the thermal valve on the water neck? If I hook the vacuum advance to ported vacuum, should I remove the thermal valve and delay valve? I've seen instructions on EVAP canisters to not hook the purge valve to full manifold vacuum, so should the vacuum canister line and advance line be on a tee together off the ported vacuum source?
Don't use the ported vacuum for ignition advance. Somebody once had a very nice link to a writeup on the details behind it. Basically, the porting was intended to improve emissions and doesn't really apply to our applications. My car runs far better using the unported line than the ported line.
It was interesting, I followed somebody's guideline here for setting the timing. Unconnect vacuum, advance to max manifold vacuum (mine was 36BTDC) then back off until manifold vacuum drops 2". Mine was 16BTDC on premium gas. Runs awesome. Well so far, I've got some other issues I'm attending to before I can take her on the street again.
