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type/octane fuel I should use. I have a 1993 200hp The book calls for highest grade fuel I can get (with a min. rating)more detergents and other qualities. We (State agency I work for)just bought a new HDPI 225 at work and the Yamaha dealer (Ronnies Marine stated we were "NOT" to put anything but reg. unleaded in. Said high octane will harm all outboard motors. What am I to believe???? thanks steve
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CCSGB,
Your question is a good one, and there is a lot of confusion on this subject of what octane to use. The higher octane fuels are formulated to burn at a higher temperature (flash point) than lower octane fuels. The higher the compression of the fuel/air mixture in the cylinder, the higher the temperature of that mixture before it is ignited by the spark plug. From what I have read on other message boards and elswhere, if you run high octane fuel in a motor that has relatively low comression, the fuel will not burn completely or as good as a lower octane fuel and therefore, carbon buildup will occur more rapidly. You also will not be getting all of the energy out of the high octane fuel, since it is not burning completely.
Your 93 Yammie 200 probably does not have any higher compression than my 2000 C115. My owners manual calls for an octane of 87, and it runs great. There is normal carbon buildup, but that is mainly from burning the oil.
Check the manual for your model engine and use what it recommends. Don't listen to the argument that higer octane fuels have more power, because they don't. They just have a higher flash point so that they can handle the higher temperature of higher compression and will not pre-ignite before the spark.
Good luck,
Ken K.
fishingkat@aol.com
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