don't use any petroleum based solvents in any of the YS engines, as they all use silcone seals and diaphragms which will be damaged by the petroleum.

Have you tried changing the brand of fuel for a dozen flights or so? It could be the different types of oils in the different fuels, some could work better than others. I have never had carboning in any of my YS's (91/110/140L/140DZ/160DZ) which have all been run on coolpower 30. Maybe try a gallon of that?

James