The airbleed screw does have a spring on it to help to keep vibration from rotating it.

As for fuel. I would go to a minimum of 22-25% oil content in the fuel. The Max-H series had Meehanite pistons in a steel sleeve and unbushed conrods. Most commercial fuels are only 18% nowadays. Duke Fox used to recommend a 29% oil content for his .35 Stunt engines (same construction) which he still makes. He also still supplies the 29% fuel for us old toots with good old engines.