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I'm assuming you have a two stroke Merc 40, and the ratio would be 50-1 or about 2.6 ounces of oil per gallon of fuel. Remember the 50-1 and when you add the fuel there will be a chart on the back of the oil can. Use the 50-1 colum.
What is the ratio of gas and oil in a 40hp Mercury Outboard motor?
Thanks, ***** ***** for my father in law who hasn't used the boat in so long he had forgotten what to put in the motor!