The question is not about detonation with 50% ethanol. It's does a gas carb have the metering block's to supply the increased fuel volume to run 50/50? I run e85 to a motor at about 12.5:1 compression. My gas carb is insufficient. I'm betting you run lean no matter how much you turn the screws up? If someone has experience with pushing the carbs limits? I would be interested.
Well in my limited experience, it's about both. My x headed 340 that I drove on the street in my younger days had a satisfactory fuel mixture with the x heads and a stock Holley 750(before the advent of hp carbs)
When I built my w2 340 with this same carburetor and the biggest #99 jets all around, it was as lean as can be.
I took the carb to a specialist in Hamburg New York(Ray Murray)
and he did his thing to it and then had perfect mixture with 68 and 69 jets in the same carburetor. He said the difference was the out of the box fuel curve was not designed for a high performance head.
I have never used any alcohol fuels, but my research tells me you need a fuel specific carb.