Oops I just realized that 5 6 7 and 8 are out of order. But the burn is the same.
I might start with a check of the engines timing.
I would be checking you're carb. I think the one side had plugged main metering jet.
My guess would be an ignition issue
This deserves more than my initial very short explanation.
The spark plugs have a very interesting pattern that just happens to match the runner pattern on most common intake manifolds. The carburetor barrels do not go directly to the associated cylinder banks.The pattern on most production automotive V8 engines is the front and rear runner on one side ties into the two middle runners on the opposite side. This is done to equalize runner length and to keep the overall engine height down. No, this does not apply to all engines and especially performance high rise manifolds but for our stock Ford 427s and Chevy small and big blocks, it applies.
Not saying Mark does not have any ignition problem but the spark plugs indicate rich mixture on 4 of them. The other 4 are dry and show little presence of combustion.
Weak or no spark will lead to wet plugs on the cylinders that receive fuel but have no spark. This is not what Mark is showing us.
Timing issues will cause plug readings to be consistent across all of the plugs.
A bad distributor cap will usually create issues on associated cylinders and having this unique pattern is very unlikely.
I suspect that the idle portion of the carburetor is functioning on both sides so the engine might idle okay however the main meter circuit for the one side is likely plugged.
Popping off the flame arrestor and carefully observing inside the of the carb while the engine is running will give you the final answer. Burping the throttle will likely show that the one side is dry and the other is metering gasoline to the engine.
I would also recommend caution in that the one side of the carb is likely running very lean and backfires due to low flame velocity is likely to be experienced. Using a mirror to see down inside would be a very good idea if you value your eyebrows.
I agree with Ronald about the indications on the spark plugs --definitely 4 are showing too rich and the other 4 running hot/too lean. He also has a great idea on the possible cause . I didn't know the engine type in question--but in the original post it seemed as if the spark plug pattern was a gremlin but almost a incidental finding. I was wondering how well the engine was running?
Captain Ronald, upon further diagnosis you are exactly correct. Compression is 145-150 across all, timing is spot on, valves are all within tolerance. So going on the advise of the supreme Commander Morland, I took the arrester off and when I burped it I found fuel only coming from one side into the primaries. I did not have a vac gauge with me at the time, but will have upon return. I had my idle screws set on 2 1/2, I ran them in until the engine changed and then backed up 1/4. However when I discovered the one sided conversation in there. I removed the carb and retired to the cave. I disassembled, cleaned and blew out again. The only thing I found was I left the top spring and retainer off the acc pump. I have replaced it and reassembled. The truly sad part is I can not get back to the boat until Sunday! I am learning to be a carb man, so this may take a while. I am confident in my work, well other than the one little mistake. However I am not confident in my super tuning abilities.....yet. I want to thank you all for the help. The one thing I have been able to count on during this project is some outstanding help from this group!