Turns out the problem I was having was from a split carb to manifold gasket.
Even though I had tried the usual spraying gt40 / wd around the carb base to check for vac leaks and found no change in rpm.
When I tweaked / pulled the carb up slightly the engine would stumble and die.
The carb gasket actually looked ok, was just a bit delaminated.
After fitting a new gasket she's running great now. Very happy.
Very rich exhaust condition caused by a lean mixture. WHO KNEW. Livin' and learnin'