I use 10% ethanol in my 261. I have the timing set right on the timing ball mark, and then turn the 'octane advance' almost all the way. It will ping if you lug it hard and will 'kick back' if you just bump the starter. I really should back the timing off a little.
If I use straight no-lead it will ping much easier.
I have never tried premium--I just can't make myself buy expensive fuel when I don't need it.
