Before you accept total defeat, QDM, bear in mind that Rotax recommend that their engines be run on MoGas when possilbe. They'll run off of AvGas, for example when high tank temperatures are expected, or when no source of MoGas is available, but the plugs tend to get fouled up by the lead if you use too much AvGas.
But that's not relevant to your Super Cub, which doesn't have a Rotax, so maybe you should admit defeat!
FFF
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