Doc, I have been going through your list today, and thought I should post the results.
Firing order correct, Plugs are properly connected and well separated.
I can't get the ignition module tested as I live in the UK, I can't find any one that tests them. Is there a way I can test it myself?
Both advance units function properly. Can't see any wires shorting out. Distributor cap is clean, no cracks/carbon.
I carried out the Coil check, the Primary side (BATT & TACH) was 0.5 ohms. I couldn't get a reading on the Secondary side (BATT & Rotor Pickup). Meter indicated a broken circuit.
Could this cause my problem? Like the spark needing to jump the gap, causing week spark under load?
I rebuilt my old carb, and put it back on, just to see if it would make a difference. -Made no change.
I blocked off all vacuum ports, and have checked for intake leaks. Can't find any. The vacuum doesn't fluctuate, its 15in hg steady at idle.
I have a clear in line fuel filter, there is no problem with fuel volume, and the pressure is about 3.5 PSI, (cranking). Both filters are clean. Gas is new 95 octane.
There is an EFE system in the right exhaust manifold, it is stuck in the open position. All the emission equipment and control gear has been removed.
Have not done a compression test yet, I did check them last year and the results didn't indicate a problem.
There is no cat, and the exhaust seems to flow well at high RPM in park.
Thank you for your detailed responses.