Greg,
I have never seen a fuel pump force a needle off the seat but Jon indicates it can be done. It's real simple to pull the top off the carburetor and pull the float off and take a look at the needle. Any modern needle would probably have a Viton tip and it should appear intact. You can drop the float into a little pan of fuel and make sure it floats.
Stuart
Stuart - there is an engineered relationship in the fuel system among the buoyancy of the float, the orifice of the fuel valve seat, and the pressure supplied by the fuel pump.
A heavy (modern foam) float; the incorrect size fuel valve seat from a generic kit; or excessive fuel pump pressure can all cause fuel level variance in a carburetor. A significant amount of any of the above (or a combination) can cause fuel to run out of the carburetor.
Examples: some generic repair kits for the Carter YF have fuel valves with orifices as high as 0.110 inch when the design for the YF used on Chevrolet was about 0.086 (maximum). While more fuel can enter the carburetor, more float buoyance is required to close the valve. And there is one company out there rebuilding fuel pumps that use the philosophy that if the part fits, it will work (kind of like some look at carburetors). We have measured 19 psi from some of his pumps that should be at 3 1/2 ~ 4.
"One size fits all" might fit, but rarely performs to the level possible.
Jon.
