Thoughts on the various additives out there. I always use 92/93 octane non-ethanol fuel for both my 2 stroke Yamaha 250 and my 4 stroke Merc 60. Using the high octane with no ethanol added, what is the best fuel additive to use??

Search this has been discussed many times.

Honesty unless you have a modified motor I think your wasting money on the hi grade gas.

If your using non-ethanol then you probably only need to use stabil if your going to store it for extended periods of time. We used to run sea foam every other tank for a clean/decarb/carbon preventative.

Most of the cocktails of additives are in response to ethanol fuels which your not using.

Thanks redchevy. The reason I run high octane is I've been told that over time the octane rating of gasoline is reduced...if you start with 92, in a couple of months it might be 87. So I'm guessing if I start with 87 in a couple of months it would be subpar...don't know, I've just been told that. Thanks again.

Octane does not just drop after a given time in fuels....at least not until also significant water condensation accumulations already have occurred and then you have potentially damaging fuel issues other than just octane levels irregardless of the fuel used being pure-gas or E-10.

I add Starbrite star tron to every fill up. I've not had a fuel related problem since I started using it.

Get the manuals out and use what is recommended by the manufacturer. Octane is the resistance to preignition or "knock". Using to high is a waste and could lower performance and build carbon deposits. the only time you go up in octane rating is when you raise compression or advance timing. As far as additives go use a good cleaner and an ethanol treatment(if you use ethanol enhanced gas) in every tank for best results. I use Quickleen and Quickare in my Mercury 250 Pro XS and have had no fuel related problems whatsoever. I think there are a bunch of good ones out there. I do believe using them on a consistent basis is the trick to their performance.

I have never had a fuel related problem and never used any additive at all.

Can someone explain "ethanol treatment" to me?

The ethanol isn't going to go away. If your going to use it right away then don't treat it at all. If your going to store it for an extended period of time use a stabilizer. A couple weeks to a month and there will be nothing wrong with the gas. If it accumulates water in it in that time frame you either A- bought gas with water already in it, B- have a leak in your tank, or C- water flowed into your gas from some other source and s stabilizer isn't going to help. Number 1 way to avoid water in fuel, store boat in a garage. Number 2 way, don't use an internal tank.

Get some fresh gas and put some in a pint glass jar. Let a fan blow across the jar for 1 hour.
Look and see how much water is in it.

If you are certain there is no ethanol in the gas you are buying, the only thing you have to worry about is condensation, and gummed up carbs or injectors if it sits without being started for long periods. I would still add some water inhibitor/gas stabilizer to every tank.
If it is possible you might be getting some ethanol, you would be money ahead to add an ethanol treatment to each tank.
I drained my gas tank in a Nitro I had a few years ago. The gas was purchased the day before. Put some in 3 different quart jars. 2 hrs. later in all three jars the ethanol had separated from the gas/oil mix, and settled to the bottom. You could see 1 or 2 tiny bubbles of water the size of a pin head on the bottom of the jar. I shook the jars around and the mixture turned grey colored, instead of the bluish normal color. It will not mix properly.
If you research it, you will discover ethanol blend gas starts to separate almost immediately. In car engines you can't see it in a steel tank. it is hard to tell it when a car is running. For some reason larger engines don't seem to have as much trouble running on ethanol as small engines.
I couldn't help but think the pickup tube is at the bottom of the gas tank where all the ethanol is settled without any oil mixed with it. That is what is primed into the primer bulb and carbs first. Pure ethanol!
Ask any small engine repair man. Lawnmowers, weed eaters, chainsaws, etc. Several have told me since ethanol has been added to our gas, their repair service has double in volume. All because of phase separation, and what ethanol does to most plastics and rubber.
I know there are some climates that have quick temperature changes or muggy, humid air. Those climates allow condensation to build up in a gas tank very quickly. And not everyone can afford to store their boat indoors. Others park in a slip which is even worse than the back yard.
I had trouble with the Evinrude 200 hp on that Nitro for months, until I found out about ethanol and phase separation.
I always add a good ethanol phase separation additive to slow the process and keep my outboard running good.
I run my outboard at least once a week, sometimes 3 or 4 times a week. So the gas doesn't sit very long.
I can afford a bottle of additive, not a new powerhead.
My 'SOSO' Humble Opinion.
Hate ethanol!