Seems a litle high relative to factory. Lemme look in the FSM. Don't think that alone should be a cause though.
And forgive me if this sounds too basic,; Was the timing and idle set with the vacuum advance disconnected?
That's a good clue its not the accel pump but the something more basic. Fuel level is the only one I don't think has been brought up yet.
Sadly. No. And I can't even give you an approximate what to look for on the Stromberg. However I agree that knowing that the idle stop screw is only 1/2 turn does suggest that this is not the issue. Putting this together with the timing and idle speed it may be that the timing needs to be reduced and the throttle position opened. I mean a little. Let me look up the factory spec before I speculate more on this.