On most of the out boards it's 50:1 but you can call any dealer or look at a merc site. They are pretty tough old motors.
50-1
What is the fuel to oil ratio for a mercury 9.9 hp 2 stroke engine?
50 : 1 is the correct fuel mixture
50;1
50:1 25litres of fuel to 500ml of oil
50:1
the mixture is 50:1
I have a 1999 Mercury 2stroke 5HP outboard and the owners manual states 50:1 Gas/Oil mixture.
50:1 I believe
50:1
50:1
Mercury outboards prior to 1966 use a 24:1 fuel to oil ratio.