Thread: 400 SBC problem - ignition or carburetion?

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Symptoms - rough running, feels as if cylinders are missing, poor power.

History - my wife and I built the car (1929 HiBoy roadster) in the early 1992. I replaced all battery cables February 2023 because the engine wouldn't crank. That problem was solved, but the engine wouldn't start. I tested all ignition wires for voltage drop, and found none. I replaced the plugs (see below) and the engine runs, not great, though.

As I normally do in preparation for each driving season (I live in PA, so that's April through October), I ran Seafoam through the engine in April 2023, but that didn't have the usual salutary effect. Thinking that the carburetor may have been affected by ethanol (as I've found in the past), I used an Edelbrock kit to rebuilt the 1405, carefully following the factory instructions and settings.

Further information:
1. Initial timing set at 12 degrees BTDC. Vacuum advance distributor.
2. Spark plugs: Accel copper core 576S, gapped at .030.
3. Plugs in cylinders four and six are perfect - clean and light brown.
4. Plugs in all other cylinders are dark and wet.
5. Using a spark tester, I confirmed that all plugs are firing.
6. Other than an aluminum intake manifold, the engine is a stock mid-70s 400 SBC.

Any suggestions or observations? What have I missed?

Thanks in advance for your time and help. I will follow this thread and respond to comments ASAP.

Dorsey