1967 Mercury 650 pre mix help?

[rodawg]

This is my first boat and I am trying to understand how the fuel/oil pre mix works. I am unaware of the actual ratio for this model engine (serial#2448808)and how to best mix the fuel/oil and what the best oil to use would be. Fuel tank is installed in the boat so I cant remove it if this makes any difference. Boat is a 1980
15ft Sundance Marine (made in Redding, CA).

Any help would be greatly appreciated.

Thanks,
Roman

 

[Chris1956]

Re: 1967 Mercury 650 pre mix help?

Roman, I believe Mercs of that era were a 50::1 gas-oil mix. Mix 1 pint of any 2 cycle oil rated TWC-III with 6 gallons of regular automotive gasoline to achieve the 50::1 ratio. In a built in tank, you need to estimate how much gasoline you can add, and put in the correct amount of oil. I do it on three gallon increments. i.e. If I can put 9 gal of gasoline in the tank, I first add 1-1/2 pints of oil.

 

[rodawg]

Re: 1967 Mercury 650 pre mix help?

Thanks Chris. That helps a lot.

 

[Fuzzytbay]

Re: 1967 Mercury 650 pre mix help?

I'd pre mix in a gas can. Check the tw-3 oil you use, some oil requires more than a pint for 5 gallons (canadian gallon) . There should be a chart on the oil mix, check it for your 50:1 mixture. It will tell you how much oil to add per gallon. Pre mix the fuel in a gas can, ( so if its 1 pint for 6 US gallons mix it up in the gas can at the max amount the can can hold) then add it to your tank. Contrary to popular belife, more oil (ie 24:1) is bad for a motor. Too much oil can cause lean out conditions in the cylinders, so while the bearings may be lubed up, the cylinder walls score. We all know not enough oil is not good too, of course.

 

[rodawg]

Re: 1967 Mercury 650 pre mix help?

Thank you. All great info.