Originally Posted by
the pope
My saito with more than 50 hrs needed bearings . The exhaust valve had some carbon that was easily cleaned up with a scotch brite pad with the valve in a drill press . Not enough to effect its running . 20% oil with a 1/4 of that castor . Just saying is all .
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.