If fuel isn't actually pumping out the overflow, forget the float bowls.

1) Check that the choke is completely off. The jets can stick in the down "rich" position. See that the do retract all the way upwards.

2) Push up the pistons in the domes. They should fight you back, but not bind in any way.

3) When let go, each piston should drop all the way to its seat with an audible thunk.

4) Use a small mirror to verify that the needles are correctly installed. The flat bottom of the cylindrical portion at the top should align with the flat bottom of the piston. I've seen people push them all the way up until they stop, and that's guaranteed untunable rich.

5) Start the motor and operate the throttle by hand. Do both pistons begin to rise at exactly the same instant when the throttle is opened?