Re: 1987 Johnson 90 hp fuel
Buying higher octane fuel is just a waste of $. All fuel grades today are of poorer quality than in the past. These crossflow engines are prone to long-term carbon accumulation around the rings. To prevent that- an annual application of Bombardier Engine Tuner is recommended. Also, they make a product called Carbon Guard, which can be premixed in the fuel tank and is supposed to reduce carbon accumulation (775629.) Both Merc and Yamaha make similar products for their engines. I prefer to use the Bombardier XD50 oil which has the carbon guard additive premixed in the container.
