Gas to oil ratio for 1966 Johnson 40HP outboard?

Answer 1

Originally it called for 25 to 1 30wt non detergent motor oil. DON'T mix modern 2 stroke oil at that ratio or it will smoke like crazy and foul the plugs. I run mine at 40 to 1 with no problems. I'm rather careful when it comes to my motors and I checked with Tenn. River Marine here in north AL to make sure. At least one of the guys there went to school for outboards and is a confirmed Johnson/Evenrude fan. If it's been sitting for a while one thing to make sure you do before you put it in the water is to dump out any old gas, replace the gas lines and before you hook the line up to the carb squeeze the bulb and flush the line from the tank out. Also it's a good idea to install an inline filter and clean out the fuel pump and carb. The great thing about the 40 hp is that it's a single carb that's really pretty simple. After doing all that to mine I put in fresh Champion plugs and it starts and runs great! Almost forgot, do not use NGK plugs in Johnson motors. The resistance is wrong and will cause intermittent miss at varying throttle positions. I love my old Johnson, I just wish it was about 40 lbs lighter and was a console control instead of a tiller. Mine is on a 14 ft Tom- Boy Tri hull and the first time I opened it up it came up on plane so fast I thought I might get water over the transom!