Reply To: gas oil ratio for a 1968 Johnson 15hp electric start

[Don]

I too, would stick with the original oil mixing specs… And yes, OMC did offer some sort of 15hp around the mid to later 60s.
Your 1956 15hp electric start may use a 6 volt battery though, not sure.
What kind of condition does this engine look to be in, can you post some pictures?
If you plan on using this engine frequently, it is best to go through all the systems thoroughly, so it will be a reliable daily runner…
For now, let’s start with compression, spark test, and draining/inspect lower unit lube…Do not remove the little phillips screw on the bottom of the gearcase skeg, or the internal shifting linkage will come apart. Remove the big fill drain screws above (or just below) the AV plate (horizontal fin above prop), and the other one on towards the bottom of the skeg.
Hopefully, you will see relatively dark gear oil drool out slowly. Milky colored lube, raw water, or nothing at all draining from the gearcase spells trouble…
Let us know what you find…