Can't believe fuel pump simply quit - -

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while merely sitting. 68 Suburban w 327 started/ran great a few weeks ago. Today - no start - no fuel to carb. Pump has no more than 200 miles on it, but 3 years old. Plenty of gas in tank, fuel lines from tank to pump and pump to carb are clear (air test), and the pump PULLS 12" of vac and holds it static. But, no push on the output side.

Have never been inside one of these mech pumps. What beside the diaphragm is in there to go wrong? Can't believe it would pull/hold 12" vac if the diaphragm were leaky. Maybe a check valve setup in there? If such a valve were malfunctioning, seems like the pump could pull vac yet push nothing. No?

I have an identical new pump here to install - would rather not use same type pump if it is likely to go bad while just sitting (am suspecting ethanol as a factor). Would you go with an electrical pump back by the tank? If so, what make/type?

Thanks for any insights.