Misfire at cruise, popping/afterfire at 3000RPM
And 6 has cracked porcelain.
Well that could explain some of the misfiring!
There are two places the wires cross, shown in this pic. How bad is that?
The cross wire isn't too bad IMO. Long runs of the wires parallel are also not good.
I assume you meant inches of mercury?
MAG PICKUP DISTRIBUTOR W/ VAC ADVANCE CONNECTED
20 DEGREES INITIAL, NEED TO CONFIRM TOTAL. FLOATS ADJUSTED IN THE CARBS.
For the moment, based on all you've posteed, lets assume fuel level is OK.
Based on what you've written, theres's a good chance the the initial timing is probably too high for that distributor.
A. Just because the engine runs well at idle in neutral doesn't mean the rest of the timing will be even close to correct.
Setting initial timing works with factory distributor because the amount it advances with increasing rpm has been matched to be correct when the initial is set to spec.
B. Setting the initial by advancing the timing until no further increase in rpm is wrong. I know its often recommended, but the reason it is wrong is without any load on the engine, the engine can be run very lean. At idle the goal is not lean but to make the most power under very low rpms. This way the engine doesn't bog or die when placed in gear.
I will follow up with another post regarding timing.
The issue also remained while driving with only the center 2BBL connected and the outboards blocked.
One possibility I can think of is maybe the vacuum secondaries aren't opening under heavy throttle, causing a lean condition.
Okay, I’ll steer my focus away from the secondaries then. I was thinking that the engine might be starving for fuel if they weren’t opening
OK. You now know that the AFR is not related to whether secondaries open or not. When the secondaries open they should provide the same air fuel ratio as the center carb.
Center carb dumps plenty of gas when I hit the throttle
You are seeing the "accelerator pump shot" which is needed when quickly opening from closed or low throttle position.
When driving at 60 or 65 mph and faster, the boosters respond to increasing throttle without the need for much if any pump shot
