just rebuilt runs bad

Still looking for some help. At TDC with a little advance the motor runs bad, has light clickity clacks, and backfires through the carb. Here's the latest based on many of your suggestions.


- Verified #6 cylinder valve overlap is within a half inch of the timing mark. It was about an eighth.
- Verified TDC using a piston stop. Right on the money.
- Verified both intake and exhaust valves closed at TDC compression stroke.
- Verified at TDC that rotor is pointing to the number one spark plug terminal.
- Verified spark plugs in proper firing order 18436572 in clockwise rotation.
- Removed new MSD6AL PN 6420 from its original location and isolated it as far as possible from any other electronics.
- Isolated orange/+ and black/- coil wires from 6AL to new Blaster Coil from other electronics
- Isolated Green and Purple wires running from 6AL to used MSD 8534 magnetic pickup distributor with mechanical advance.
- Grounded 6AL direct to battery negative
- Powered 6AL direct to battery positive
- Locked out mechanical advance on MSD distributor.
- Compression is consistent between 135 and 145.


Based on everything I've told him the builder says he does not believe it's a problem with the build. He said they took notes when they degreed the cam and everything looks right. TDC is where it should be, valves closed on the compression stroke, rotor pointing to #1. He thinks I should focus on the ignition, which I did after work today as noted above.


Ruling out:
- Sticking valve or bent push rod. It runs too good without any tapping or backfire at 60 degrees advance. Compression is even (although someone suggested it may be a little low for my setup) (comp cam CL-20-670-4 .474 lift @ .050, 233/240, 110 separation)
- Spark plug wire-674s are new MSD 8.5 super conductor.

Other observations:
- Half of the spark plugs tips seemed to be dry and black the other half were wet and black (more of a sheen)

Concerns:
Used distributor. Noticed some silicone around the one side of the pickup. Had some light surface rust that I cleaned up.

Thanks for reading.