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Ok, will enrichen the carb however this is almost stock 383 not a 440. Also the plugs show a rich mixture - but that can be misleading as I do almost only city miles.
Distributor may be the culprit but I have no spare to swap.
Engine has 2000 miles and I always measure compression when hot.
I have a spare ignition box (stock blue one) can swap it to give it a try.
Before resto that engine had 7.4:1 CR so I know how a lo comp 383 drives. Mine loses rather some torque than power.

PS
It's not a vapor lock, I can spin it to 5 grand no issues, no fuel starvation.



I was going to suggest trying to swap a distributor , but realize that you are in Poland so that is not so easy. You wouldn't happen to have a points distributor ?

Swap in the blue box , reset the timing , whenever you change those boxes the timing moves.

Which electronic distributor do you have , an old one that you had to weld the slots smaller or the new adjustable one ?