intermittent misfire

[K20-Bowtie]

Hi folks,

I have an intermittent misfire that is puzzling me:
• 1972 Chevy K20 with 350 small block
• Delco HEI distributor
• Eldebrok 1406 carburetor with newly installed pressure regulator

Actions taken:
• Installed new plugs and wires last week. Old plugs were black and smelled rich
• Installed deadhead pressure regulator
• Timed engine at 12 degrees BTDC
• Adjusted jets on Eldebrok 1406 using vacuum gauge - vacuum around 17psi. Not any experience with 1406, but jets are within a turn from being totally closed (seems odd to me).

Observations:
• Intermittent misfire. Noticeable around 1200 rpm. I have dual exhaust with no cross over and observe misfire from both tailpipes.
• The misfire can be explained “runs along with intermittent, short surge”

I really don’t want to start throwing parts at the problem, so I am looking for additional troubleshooting ideas.

Thanks,
K20-Bowtie