fuel issue after car sits.

I blame it on the modern gasoline. Gas is not what it used to be! I have found a new fuel pump check valves leak after about one month of use. The check valves keep the fuel from going back to the tank. Small leaks let the engine get fuel to run, but do not hold back when parked for long periods.

The low vapor pressure of modern gas forces the fuel back when hot. It also evaporates and goes sour easily. The fuel solvents and ethanol kill seals. I have given up, and just prime an engine with a spray of WD40 in the carb. It has only been about 5 years that this has been a problem for me.