I have recently rebuilt a '57 Fastwin 18 hp (New Rings, Ignition, Carb, Lower Unit reseal, Water pump impeller, all new seals and gaskets.
I'm currently running it on the 1st tank with a mix of 16/1 for "break-in". Should I switch to 24/1 after break-in, and if so, when is "after break-in...