[drolston]

Nothing keeps gas from coming out of that hole where the accelerator pump plunger rod enters the float bowl. That felt washer is only there to keep dirt from getting in; there is no pressure seal because the float bowl must be vented to atmospheric pressure.

So, your test proved that under low fuel pressure from the fuel pump at cranking speed, the float needle shut off fuel at the correct level. When running, I suspect that fuel pressure from the fuel pump is exceeding the pressure that the float needle can withstand. Anything over 3.5 psi can cause problems. I use a pressure regulator set at 2.5 psi, and that is still plenty of flow for drag racing (just kidding; don't do that any more).

If too much pressure is the case, the bowl will fill too high and tend to flood the engine. It will run really rough. You will probably have a strong smell of gas under the hood, or even in the car.