Tuning a carb for 1st gear performance

I knoe it may sound obvious, but check your fuel pump, and like you said, look for vacuum leaks. If its timing, then it would have to be off quite a bit inorder to immediately die when you give it a quick, full shot at the throttle. I agree, the single plane manifold hurts low end on a lower compression street motor, but its -not- the heart of the problems you are having. Check fuel pressure if possible.