The needle valve adjusts the engine for the best air/fuel ratio for proper combustion so only the combustible portion of the fuel is taken into the equation,which is how we tune our engines.We shouldn't stretch the oil content to 95% as an example!! Its more like saying that 18% oil content performs better than 20% oil content!!The fuel/air mixture for both fuels at optimal performance is equal except the fuel with less oil will have less lubrication available. The amount expelled by the breather is minimal compared to the amount blown out by the exhaust.