It's easy to make the adjustment when one doesn't have to take the carb off and apart. With my QFT 4150 clone, I have to take it off, take the float bowls and metering blocks off to change the idle feed restrictors, emulsion tube restrictors, power valve channel restrictors, main jets or power valve. At least the idle air bleeds, high speed air bleeds and accelerator system can be done externally. I bought a set of five top cover gaskets for the Edelbrock, part #1499, when I was tuning it but only had to use one.

Is the stumble from stop light with a normal acceleration, when you stomp on it or both? Changing to an even lighter spring may make it worse, but try it and see.
It may be the pump system or you could leave the lighter spring you have in it now and try a one size larger jet. If it stops the stumble great if not go back to what you have now and we'll have to try another approach.