Been in the small engine business for almost 25 years.
Last year (2014), over 85% of our repair work has been fuel system related. Much of that due to staled fuel or fuel storage problems.
In my own personal opinion, based on the typical year's worth of repairs (usually averaging about 2100 tickets a year), it really doesn't make any difference whether it's got ethanol in it or not. 2 reasons I believe this. One, in 2010 a local fuel station started carrying E0 fuel, IOW, no ethanol. At first I didn't believe them, so I bought fuel and tested it. And every time I tested, it was correct. Zero % ethanol. From time to time I'd get a batch with less than 1% but that is still nothing. A LOT of customers were pointed in their direction thinking that perhaps I could try to help their problems with fuel system issues. But guess what? They still showed up within a year's time needing carb cleanings or the like.
Reason #2 is this. The gas stations are not required by federal law to label fuel as "up to 10% ethanol" unless the fuel is 7% E or higher. That means "non-ethanol" fuel that contains up to about 5.5% can be labeled as "pure gas". Also verified at another station local to work by using the test strips.
It is not so much the Ethanol that's causing the problems. It's a combination of things. Sure, phase separation causes issues but it's a very small issue in the grand scheme of things when dealing with all the fuel system problems. What I'm personally seeing in my area is lack of education and/or stubbornness. There is not one doubt in my mind that today's fuel is junk. But then we need to ask what is different between today's fuel and fuel of "yesteryear". Used to, we could put a gallon of fuel in a gallon jug and it could sit for up to a year and it'd still work fine. This is not the case now. And for a lot of reasons. First reason is that fuel systems have become MUCH more sensitive over the last ~10 years. Thanks to the US EPA's mandates and requirements. They all burn fairly lean now and have for a while, at least compared to the old 5hp briggs and the like; which would run on beer or anything else for that matter. The passages inside the carbs have gotten so small that they plug MUCH easier. Secondly there is no doubt, at least in my own mind, that fuel is designed for one thing. Cars and trucks. But cars and trucks have had electronic fuel injection for over 2 decades now. EFI is much less sensitive to fuel quality due to it's basic designs. High pressure. Where a carburetor relies on a very small pressure drop to draw fuel through a jet, uphill in a lot of cases. Any restriction is going to cause problems. The fuel that we have now, formulated for cars, evaporates...and evaporates FAST. Get yourself a quart jar and put a mark on it about halfway up. Then pour some gas into it, stopping the fuel level at the mark. Leave it sit outside away from anything that can knock it over and obvisouly away from spark or ignition sources. Come back an hour later. About 15% of what you poured in will be gone. If it's a warm humid day, watch the jar closely and you'll see water vapor on the outside. Evaporation causes a temperature drop which causes vapor to condense. It also condenses inside the jar which "clouds" the fuel and if you let it sit long enough, it will gather up at the bottom of the jar as pure water. I used to have some pics of testing this on my own time, deleted them from the phone. But this is the same processes that happen in small engines. The fuel tanks are all vented, which allows moisture to enter as fuel evaporates. That is why you're seeing ventless fuel cans (which I hate).
So with all the problems I'm seeing-at least in my area-(mid south, US), the only suggestion I can offer is prevention. In other words, don't let the fuel sit in cans for more than a few weeks. I tell folks not to store it for more than 2 weeks without using it up, which might mean going with a smaller gas can. Or using the equipment more. Whatever you can do to keep it from going stale. I've noticed on my outboard (4 stroke 25hp Yamaha) that if the fuel sits in the 3 gal tank for more than about 2 weeks, it won't run right. Still runs but not right. I have to make sure to dump it out, usually into my Mustang, if I'm not going to use it up. If I let it sit for a month, forget about it idling. It usually means I've got to pull the carb and clean the pilot jet. Those passages are tiny and plug really easy. These types of experience is what I base my suggestions to our customers on. At this time, I believe that there is not a single additive on the market that works...and I've tried a bunch. Phaser, Yamalube, Stabil, ain't found one yet that will do what it's advertised to do. The Phaser rep comes by once a year and takes a quart of gas in a glass and pours water into it. Of course the water goes directly to the bottom. Then he puts a few drops of his product in it and shakes it up. The water doesn't settle to the bottom now. He says his product eliminates water. He is full of it. The water is still in there and if I let the glass sit for an hour or so, it'll separate right out exactly as it did before. Snake oil-all of them, IMO.
Think of today's cat-pee gas as saltwater. As it evaporates, it leaves the stuff behind that nobody wants; as saltwater evaporates is leaves behind the salt and other unwanted stuff. Same principle with the exception of what is left behind when the gas evaporates, what is left is unusable.
I stand behind my opinion that prevention is the only reliable cure.
