I have wandering the highways and byways of the US in a RV for a couple of years and by necessity have had to use a variety of fuels and although I usually stuck to 10% I too had to fiddle with the needle most times I changed brands.

I suspect the type of oil used changes the flow rate through the needle valve. I was flying 3d so max rpm was never an issue and I never bothered with the tach to check it.