Denny -
The Viton (neopreme) in the fuel valves does the same as in the diaphragms (gets hard after being in deathanol and then allowed to dry).
However, the time-to-failure is longer, due to the function.
The diaphragm has to flex to function, as does the skirt of a "normal" accelerator pump. The neopreme tip of the fuel valve does not have to flex, so hardening does not cause failure of the fuel valves.
Modern fuel valves fail due to the manufacturer eliminating the "staking" task in their manufacturer. I have covered this, and its solution previously.
Jon.
