hmm, a lot of misinformation going on... :roll:
1969... likely this motor was designed to run on leaded gasoline. they used to put lead in the gas primarily to improve its anti-knock abilities. regular leaded had an
AKI of at least 89. so, you should run a gasoline that has at least an AKI (what we use for octane rating here in the US) of 89 in order to fuel it with a substance that matches the knock resistance it was designed for.
now, ethanol.
first - they say "ethanol collects water!" - yeah, it will absorb more water than straight gas, but it will take many months before this becomes a problem. so easy fix: don't mix up more than you need and leave your gas sitting around for many months.
second - they say "ethanol eats old rubber and clogs stuff up!" - yes, old rubber fuel supply parts are incompatible with and can absorb ethanol, leading them to swell and degrade. easy fix: replace the fuel lines on your motor and put a carb kit on the carb. takes $10 and 10 minutes to replace the lines with new ethanol compatible ones. carb kit might be a little more complex, but still isn't bad. (make sure the carb kit is recent production, not NOS)
i have been running E10 in all of my small engines since it came out without any problems because i replaced the lines where required and i don't let gas sit in the tanks.
so to answer the OP's question directly: 89 octane E10 should be fine, assuming you replace the old gas lines on that motor (which you should do anyway) and don't leave gas sitting in the tank (which you shouldn't do anyway)
kfa4303 said:
Using higher octane fuel is actually less than ideal for these old 2-stokes as it delays detonation ever so slightly causing combustion to occur fractionally later in the cycle thereby decreasing performance slightly.
This is incorrect. There is
no detonation in a properly running internal combustion engine.
kfa4303 said:
Plus, high octane didn't even exist 50 years ago when the motor was made, so it was never meant to run on it.
While the outboard motor may not have been designed with a high compression ratio to take advantage of it, they did indeed have high octane gas 50+ years ago, such as the aviation gasoline rated well over 100 octane that was widely used during World War II.