Originally Posted by
airraptor
Prop you're correct they can swell up causing it to run poorly. I race all of my YS engines on anywhere from 20 to 75% nitro and no real build up of carbon on the exhaust valve like other engines do. The OS engines are the worst at this
I have seen as high as 40% nitro but haven't seen 75% nitro used in a YS engine. I have used as low as 15% and they run just fine. Nitro by itself does not add to the combustion process. At the low end nitro aids in a reliable idle but much beyond 15% doesn't do much to improve the idle. At the upper end the nitro releases an extra oxygen molecule which allows a bit extra fuel to burn during the combustion cycle. Since the YS is a naturally aspirated (engine vacuum) carb intake there is limited raw air that can be drawn into the motor. The extra oxygen molecule supplied by the nitro allows a richer fuel setting however once the saturation point is reached of available oxygen vs. available fuel any additional fuel/nitro is simply pumped out the exhaust. The only benefit at this point would be the cooling effect of the un-burnt fuel. Personally I doubt anything above 50% nitro would serve any purpose and simply be a waste of money.
Dennis