Idle falling off then dieing

[justinp551]

Been tuning up a 68 2000 and done a bunch to it but having a idling problem. When I got the car the idle was up about 1400. Well I know why it was us so high as it won’t consistently idle down low. Here is what’s been done since I’ve had it…
B cam
Carbs cleaned, checked and balanced repeatably
East coast elec ignition
Headers and full exhaust
New plugs and ignition system
Valves adjusted
New fuel filter
Checked comps 155, 155, 160, 155
Checked and got a dribble out of thermo fuel valve on carb
Timing set to 16 at 6-700rpm w/ vacuum discon
Intake checked for vacuum leaks
I’m sure I’m missing a few items but here is what’s happening
Whether the car is warmed up or cold the idle will slowly drop off and die. When it’s warmed up it will idle at 1000 about 1/3rd of the time. But the rest of the times it will start idle at 1000 then slowly drop off and die in about 1min. Only think I can think is pump is underperforming at idle and not filling bowls but when I boil throttle it comes right back for a 10sec or so. I’m at a loss on this. Any suggestions or other ideas to look at?
Thanks

[Bwk2000]

If once above 1400 rpm’s everything else works as it should (power, acceleration, no carb or exhaust backfire, no bogging down, no pinging, etc), then the problem is most likely a vacuum leak.
Recheck the intake manifold, vacuum advance line/connections and carb throttle shafts & flanges. Spray some carb cleaner on each as it’s running and see which one changes the rpm’s momentarily.
Might also want to check the condition of the oil filler cap and dipstick seals.

Normally, I would have also suggested checking the carbs for a sticking or faulty needle valve, piston or float, but if you’ve checked, cleaned & balanced them repeatedly, I think you would have already come across that.

P.S. Welcome!

[Gregs672000]

Good solid suggestions from Kai. Plugs look like...?

[redroadster]

Whats it do if you choke it when it starts to die?
Turning torque is close to normal ?
Sure cam timing is right? probably is with the compression settings ( was that completely cold test ? Its important for the idle
What does it do if you advance the ign timing ? or retard
Old gas ?
Or the idle circuit is clogged
All cyls equal power ( pulling plug wires running ( careful)
Idle is a engine load sitseation