Hydro, with the YS 115 my normal mix was 40% nitro, 20% synthetic oil and 40% methanol. You are however correct that the 115 uses a pressurized fuel system that has the tank at 9 psi. My YS 140 has an actual pump that is driven my the intake pushrod and uses medium fuel line as well. I have however run up to a 1.2 (20cc) 2 stroke glow engine using only muffler pressure with medium tube. I don’t doubt that your 11cc boat requires the larger tubing, only that your situation would be the exception and not the norm.