I am very confused about gas to oil ratio's. The owners manual for my 1958 evinrude fleetwin says to use a 1/2 pint per gallon. With 8 oz in a 1/2 pt and 128 oz in a gallon, I think, that is a 16-1 ratio. However I see people on here and elsewhere stating to use 20:1, 24:1, 40:1, etc. Is it...