Originally Posted by Propworn

So many things effect the heat at the exhaust. Fuel mixture rich/lean, load on the engine etc. that it is quite possible to get away with a carbon based lubricant in the fuel for four strokes with little or no build up in carbon deposits. All that means is your running the engine reasonably loaded with a good fuel/air ratio. Congratulations your doing it right.

YS's recommendation of pure synthetic has more to do with damage to the silicon parts in the fuel regulator than anything. Yes it also helps reduce/eliminate those carbon buildups. I know that the team from Japan at the world scale championships could not get pure synthetic in a high nitro content so they ran theirs with synthetic/castor blend with 20% nitro and cleaned the regulator parts after each run with 10% pure synthetic.

The YS ran fine on the synthetic/castor mix but they did not want to chance leaving the blended fuel in contact with the silicon parts in the regulator.

Originally Posted by Propworn

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