Manifold vacuum is always operating (vacuum persent). Ported vacuum will only operate when the throttle blade(s) open.

Is the hose connected to the passenger side port below the choke housing?

 

Everything is ported off the carb body with the exception of the brake booster, obviously. That's how it was when I got it. I don't have a vacuum canister however. Should I get one and if so, what will run off of it? Not sure that would help but maybe it would alleviate the loss of vacuum under hard braking.

 

Tomorrow I'm going to isolate the brake booster. I think the lines look good but I suspect a bad booster. It is the original '77 and my brakes do feel kind of mushy.

 

What is 'everything'? Only the distributor should be on the ported vacuum source.

Vacuum canister is only used for certain components like cruise control and emissions.

I find it hard to believe you lose vacuum while hard braking. Do you hear a hissing noise when you apply the brakes? Do the pedal comes up on its own?

 

O.K. "everything" is an overstatement. All ports are plugged with the exception of the vac. advance.

As loud as my engine is....I'd be lucky to hear a GE J404 screaming next to me. LOL. So...no, I can't hear any hisses. I'll try checking the booster on startup today.

I'll also try the torch trick and I'll post my results.

 

brake booster wont make your brakes mushy, if your booster is not working properly than it will be difficult to stop, if you have to pump your brakes, than youve got air in the lines, or a bad master cylinder.

 

The brake booster tested OK today. I haven't replace the line yet but I cannot detect a leak with starting fluid or by eye or ear.

When I started the engine it took off immediately to 2000+ rpm and kept racing. Choke pulloff is working fine and is calibrated to factory specs. Choke does open ok and once the throttle is depressed it drops to low idle ok. It seems my linkage is over rotating past the high step of the cam on startup. I didn't know that was possible. Difficult to see what's going on as there is a baffle or shield around the choke area which I'll have to remove to see better.

This thing was performing flawlessly on the bench when I initially set everything up and ran beautifully for a while on the engine. Now all these issues keep popping up. I'm really growing tired...it shouldn't be this hard for a simple 2bbl.

 

Just went through the exact same thing. The blue vacuum tree was real loose, and since I have all the paperwork since new, I know nothing has been done in that area. It must have been loose from the factory as there is a ton of crap that has escaped from the threads and pooled up back there. Looks like an oil leak.