Still having idling issues!, Less, but still some Options

[detective_snakes]

Hello! Yes yes! I've at least somewhat fixed the problem the mechanic handed me. I replaced the carburetor that was spitting fuel everywhere, cleaned up the battery terminals, and it starts! However, I'm back again to the issue where it doesn't idle for very long. I got it to idle a hell of a lot longer than the mechanic did, which is nice, but it still does die. So, up until now, I've...

- cleaned the fuel tank
- installed new fuel hoses (rubber, not the metal ones)
- installed a new rotary fuel pump + filter
- cleaned the hose junction
- balanced the carbs, tuned them to something that *should* at least work (zeroed, 1+1/2 turns out, 1/4 turn back in)
- installed new carburetor/manifold gaskets

The left carb still 'burps' sometimes and spews some white smoke. I suspect that I need to adjust the timing. In the meantime, do you figure I should try different distributor cables, a new head temp sensor...? I can't really think of many parts this could be. I already replaced the distributor as is, plus the ignition coil and a few wires.

Also, I'm sure it's fine, but only one carb is hooked up to the dizzy for vacuum. The other one I can just leave open?

Again, a massive thank you to everyone who helps. You are lifesavers.