I have the same chart Tubs has posted but I totally ignore the OMC recommended 24:1 mix given for the earlier AD and CD motors and stick with the original 16:1 mix for the older models. The 50:1 mix for the ’64 and later motors is OK as they all had needle bearings on the rod.
Notice to they say ’50:1 mix can be substituted for 24:1 mix as long as Johnson oil is used’. Was it possible the powers that be at OMC realised that sales of new six horse motors weren’t as good as expected and lots of their older motors were still being used regularly with no end in sight? Realising that a satisfied Johnson customer would probably come back and buy a new one again, slowly but surely eliminating the old motors off the face of the earth by purposefully and deceitfully shortening their life span would guarantee increased sales and profits and everything would be peachy keen again. After all, why wouldn’t they recommend the same 24 or 50:1 mix for the old TN series of motors? Possibly because they knew they would need replacing soon anyway or new parts for them were just NLA from their dealers.
Possibly I’m a bit too suspicious but I do have a box full of badly scored pistons I’ve collected over the years and the majority of them are from the 5.5 and six horse lineup. Sure, their are other causes but I also have a Fleetwin 7.5 crank and rod sitting here with close to an 1/8″ clearance on the lower rod journal. The rest of the motor was pretty worn to and I suspect it was caused by using a too light gas/oil mix.
As for the original question, stick with the recommended 16:1 mix and enjoy your summer! After all, oil is the lifeblood of any motor and is the cheapest thing you can put in it. Trying to save a few pennies now might cost big dollars later. Don’t be stingy with the oil as too much is always better than not enough!
