A good functioning primer can develop enough pressure to frequently unseat those sticky valves. But then they may remain open, starving the idle circuit for fuel. The 1934-’35 Evinrude Sportsman had the same problem. The check valve is necessarily at a low point in the fuel circuit. So it has a high likelihood of retaining fuel. Removing it to drain the line sometimes results in the sealing disk being lost. I know of several cheap trade in motors that would not idle that were "cured" by installing this (then) five cent part.
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