The engine is still running fine after 50-55 liters of 95 octane gasoline mixed with 5% (1:20) scooter oil (mineral) it still performs as the first day of conversion. all shiny and oily inside.

I find it safe to run 5% oil in this engine. no visible sign of wear, not even on the bearings after a respectable running time... I changed spark plug just once..

my only suggestion is to rig a venturi on the walbro carb to stop fuel spraying occasionally from air intake.