DeputyDawg,
I recently read an article in a trade magazine while sitting in a doctor's office that stated a test conducted of ethanol gasoline indicated that stored fuel would begin to lose it's original octane rating after 30 days and that the loss would continue for some time. It's my understanding that any gasoline will lose it's potency after time, but the test reportedly showed that ethanol laced fuel begins to lose that more quickly. Secondly, the alcohol tends to make moisture collect more rapidly in fuel that contains it. The article stated that fuel stored in a location that has significant temperature swings from warm to cool and back again results in more condensation forming inside the container, particularly after the container is opened to pour out some of the fuel and in the process, fresh outside air is allowed inside to be capped up and go through the process again.
I recently had a 2.5 gallon container of fuel that was about 2/3 full that had been stored since late fall last year. When I opened the container, the odor of the fuel inside was very strong and didn't smell much like gasoline. I decided to use that stuff for rinsing out my oil drain pan and cleaning up after oil changes. I always try to fill the tanks on any of my vehicles or equipment that use it before storage, and it's my practice to treat that fuel with SeaFoam or Stabil if the engine is not going to be started for some time. I have a twin cylinder 5 horse Briggs engine on a yard tractor that had been parked this way since last August. I had to drain the fuel tank and put fresh fuel in the tank to get it to start and run the other day. Thought I wasn't going to get it to fire at all.
Drained the carb, allowed it to fill with treated fresh fuel and sit for overnight, then got it to start.
I have a friend who lives on the east seaboard where they are selling mostly 15% ethanol fuel these days, and he says he really has a struggle with all of his engines that are carbureted. I know you can read anything, but I've read several discussions about problems resulting from the use of alcohol in fuel. The stuff doesn't produce as many btu's as does gasoline without alcohol, which is why fuel economy is generally somewhat less when using it. I personally don't like it. We have only been pretty much forced into using it here in SE NM, right in the middle of the Permian Basin oil fields and where gasoline is refined and distributed to the country all around us. Interestingly, we also live in an area where there are several alcohol production facilities that use milo (grain raised in the area) to produce the stuff. And to add insult to injury, fuel prices are higher here than anywhere around, New Mexico or Texas!
Based on my experiences, I no longer keep more than one 2.5 gallon container of fuel on hand for my mowers, etc. I prefer to use that and go get fresh fuel rather than keep two or three of these containers handy.
I also routinely add the recommended amount of Sea Foam or Stabil to the container when I empty it prior to refilling. I do that year round, rather than just in the fall as I used to do.
My explanation is probably not very scientific, but no gasoline will last forever with out some degradation in quality. Ethanol fuel won't last long at all, and tends to collect moisture worse. It's hard on some rubber and plastic products, and it tends to create a whitish build up on internal parts and stops up jets and passageways in carbs and mess up needles and seats, etc. That's my experience with the stuff, for what it's worth.