Older 2 stroke Motor fuel to oil ratio

I have seen where a few people have mentioned they add more oil to thier fuel on older 2 stroke motors. I understand the concept, but have not seen a standard of how much more oil to add.

Also, my particular motor, a 25hp Evinrude (1974) states the use of 91 octane fuel. Was that because of the amount of lead in the fuel in 1974? What would be an acceptable octane to use? Only 87,88 and 92 are available where I live.

I had the same motor in a 76 model. I ran 50:1 with a quality oil. I also run premium non ethanol fuel in all my small engines. Good mix and that motor will just keep running.


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Oil now is soooooo much better than the oil then. Use regular 50:1 and you will not have any problems.

More internet myths. No reason to run any more oil than 50:1 unless you like lots of smoke and black sludge dripping out of the exhaust when the rig's sitting on the trailer at home. That and the extra unburned oil that is pumped right into your favorite waterways.

turbotodd said:

More internet myths. No reason to run any more oil than 50:1 unless you like lots of smoke and black sludge dripping out of the exhaust when the rig's sitting on the trailer at home. That and the extra unburned oil that is pumped right into your favorite waterways.

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Good point.