I got a copy of the original owners manual for this motor and it says to mix 1/3 pint oil per gallon of gas. That would be one quart per six gallon tank which I believe would be 25:1. It also says to use SAE 30 outboard motor oil or SAE 30 grade automotive oil. It says "use only the recommended oil to gasoline mixture ratio regardless of the claims made for some lubricants. The person I bought the motor from said he was using 50:1 mixture of 2-cycle oil, or one pint per 6 gallon tank. This was also recommended by a boat dealer I called. Perhaps there is a significant difference in oils available now as compared to 1959. I'm hoping to hear from others who own or are experienced with this motor. What works best?<br /><br />Thanks