Our local gas station just started selling non Ethanol 91 Octane gas. I have a 1999 200 HP Yamaha and have always used 10% Ethanol 87 grade also the owner manuals specifics 87 grade. I use my boat regularly and use ringfree and Marine stabilt so the gas does not sit long. Those of you with older outboards are ya'll using the non ethanol 91 grade or staying with the 87 ethanol grade. I have see what ethanol can do to engine parts if they set up for a while but I do not want to do damage to my outboard by running a higher octane gas if the older outboard will suffer from using the higher octane.

I am interested in the same thing, I have a 1981 115 Evinrude, just got it. You might want to re-post this in boats and motors.

Stick with the 87

Yamaha specs 87 and I have run nothing but 87 including E10 in my 1989 Yam 150 ProV since it was new along with Marine Stabil. No probs,
Why waste $ on 91.

Mineola has 87 octane non ethanol.

Run what is recommended by your manufacturer for octane rating. Higher octane burns slower, causing soot and carbon build-up when used in engines not rated for it. Replace all fuel lines and pump parts with ethanol resistant lines and parts from fuel tank to motor. Keep fresh gas at all times.

91 will not hurt the motor. It will have slightly less power but you wouldn't be able to feel it. You may notice the engine running smoother and quieter is all.
Higher octane burns slower and cooler and in car engines and allows for more timing advance, usually around 5 degrees or so faster.

People often think higher octane premium fuel will make their car, boat....faster. Just the opposite. It burns SLOWER and is only necessary for a higher performance motor that needs the slower burning fuel to avoid preignition(pinging) that a hotter/lower octane fuel will cause. The low octane fuel ignites to early in the ignition stroke and that pinging noise is absolutely harmful to your motor. The fuel is igniting to close to top-dead-center(piston all the way up) instead of 15-20% past TDC which gives optimum power. Good news is higher octane fuel will ignite later than your engine was tuned for and you will sacrifice some performance but it will not harm your engine. All that to say I run what my motor was tuned to burn and use additives to minimize the potential problems of ethanol. Course if you can buy 87 ethanol free like @ Lake Fork buy it!