Bobpaul got me to thinking about older moter oil mix so I did a little research on this as I could remember something about use 40:1 mix on some of the early sixties and up motors. This is a thing that a good friend of mine sent me as he is an expert on vintage motors and hope it sheds some light on this subject. I e-mailed him and this is what he sent me. One of the most commonly asked questions is how much oil to add to the gas. A few rules of thumb that I go by - some people may have different opinions but this works for me and I haven't burned up any motors. MERCURYs - ANY non-high performance Merc made after 1960 can handle a 50:1 mixture of fuel and oil. Racing motors will need more oil. I run 20:1 in my smaller Merc racers. Newer V6 high performance engines might need more and some require av-gas (100 octane). POST-1964 JOHNSON/EVINRUDE/GALE - The official stance on 1964 and newer OMC engines is to run them 50:1 and it's a good rule of thumb to follow on the bigger motors. OMC also renegged on the late 1980s 100:1 recommendation on the smaller (4-35hp) motors, bumping them back to 50:1. I've found that the smaller (3, 4, 5, 6hp) motors from post 1964 up into the mid-1970s may appreciate a bit of extra oil as they still have some bronze sleeve bearings. I run 40:1 in my '72 4hp, as I have a pile of holed blocks, burned cranks and twisted rods that were run at 50:1. 1960-1964 JOHNSON/EVINRUDE/GALE - 18hp and up can run at 40:1, as they are mostly jeweled motors at this point. Anything smaller run it at 24:1. Pre 1960 - any size, run it 24:1. If it's used for racing or high performance, double up the oil... CHRYSLER/FORCE - All Chrysler/Force motors can run at 50:1, except for anything used in a high performance application - double it up. ALL other brands - pre 1960 run 24:1. Pre-WWII run 20:1. Most brands post 1970 run 50:1. Also, 2-stroke outboards are not lead dependent, so don't waste your money on lead additives, regardless of the age of the motor. This probably doesn't cover all cases and applications, but it's a start. Some guys who know their motors well may lean out the oil a bit - I do it myself on some motors - that's your call. When in doubt, err on the side of caution and add a bit more oil. Always use good quality oil, minimum TCW-3 rated, and mix it with good quality mid-grade gas (high test not necessary!). On older (pre 1960) engines running synthetic oil, keep the ratio the same, as the oil does more than lubricate when there are bronze bearings involved.