I am definately NOT an expert on Holleys; but if you were running a brand of carb with which I was familiar, I would suggest that some crud from the pump change has partially blocked the idle system.
Over time, sediment from the fuel forms on the inside of fuel lines. When the fuel lines are disturbed (ie removing fittings to change a fuel pump), the sediment is dislodged and flows to an opening smaller than the sediment (often the idle jet in the carburetor).
I would suggest cleaning the idle circuit in the carb.
Yes, the carb is too big for the application; but I vote with ojh - if this were the problem it would have arisen upon the initial installation of the carburetor.
And just for the record, I would install bushings in the throttle body of the Stromberg WW and reinstall. Other than the throttle body wear due to the aluminum throttle body, the WW is one of the finest two-barrel carbs ever built, at any price, anywhere in the world.
Jon.
