I have done all of that within the past month, except for vacuum tuning the carb. I've always done it by sound. How would it be done with the vacuum gauge?

 

It's simple. First you need a gauge of course, and a source of (constant) manifold vacuum. Usually a port is available on the carb, below the throttle plates Disconnect and plug distributor advance vacuum hose. Engine warmed up. Idle RPM at spec. Make sure your float level is OK., timing is already where you want it, etc. If you change your initial advance, adjust valves, etc the idle mixture setting will probably move so save this for last. Even a new fuel pump would might change float level, that would bugger idle mixture, etc.

If the engine is tuned well the sweet spot will be a narrow defined adjustment band. Use the tach and vacuum gauge, but trust your ears at that point. Simply adjust the idle mixture screw(s) equal amounts for the highest vacuum indication achievable, and back off a little for smoothest idle, you'll hear it. (Favoring a slightly rich mixture.)

You'll likely have to adjust RPM again once you get the mixture set closer, a back and forth kinda deal. Using a gauge will give a good indication of engine health, timing, and carb setup. They are a must-have in my book.

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That was my experience. Where I messed up was, kinda cheaped out on the rebuild at the end. Big mistake. Used a junkbox carb and dizzy and slipped damper. Nobody could time it with a light at that point, mine died years ago and never replaced it. Timing with a vacuum gauge works well; but didn't know that then.

While I sprang for a full engine build it got spendy for me. New pistons, rings, rods, ground crank, oil pump, etc, but it never ran right. A Pertronix perked it up nice. Still not there, though. A new Holley, it liked that! About the same improvement again roughly. Setting it up correctly, even more. Finally... New dizzy, plugs, rotor, battery THEN the engine was ready for carb tuning and distributor curving. The Y blocks have about the smoothest thumpety-thumpeta idle you ever heard. Whoever said carb problems are 90 percent ignition related was exactly right! Coulda saved all that time by doing it right from the git go!

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Ended up doing a number of things chasing the problem. I ended up replacing the electronic ignition module right off the bat. It gained quite a bit of torque in the low-mid range, but had absolutely no effect on the hesitation or cutting out. Then I played around with the vacuum lines, switching around between ported and manifold for both the EGR and V-advance. While this effectively eliminated the hesitation (it still comes around under very specific circumstances), I was completely unable to induce the top end/shift power loss. However, this created a new problem: detonation. I'm in the process of adjusting the vacuum advance dashpot, and it's slowly lessening the issue, but it still wants to start acting up again after extended freeway driving (~30 minutes or so). Base timing is currently set between 10-12 degrees of advance, so I may dial that back towards 8.

 

EGR in general reduces tendancy to detonate. If switching vacuum lines for EGR caused the ping that may be why. Both the carb and distributor advance curve need re-tuned to run without EGR.

I wonder if the EGR system has a vacuum leak or other problem?

 

Alright, time for an update. I solved the pinging issue when I discovered that my timing light was completely shot, and that the distributor was set at nearly 20 degrees for the base timing (No clue how it was still idling well). Going to vacuum tune the carb tomorrow. If that doesn't solve the hesitation/bog issue, I'll have to assume that there was a mechanical failure inside the carb and inspect it as such. Either that, or I have a phantom vacuum leak, which I doubt.

 

Another update:Vacuum tuned the carburetor and correctly set the advance. The bottom end hesitation is now more of a rolling bog than the engine dying outright, but it's still there. It's still dying on WOT upshifts too. It'll rev to redline, shift, then cough and choke before dying completely. Seems like the knock is back too. My money at this point is a vacuum leak, but again, I'm not sure.