I gave it a try, two weekends in a row. I have some advice to pass on to those with fixed fuel metering systems, like carburetors, i.e. if you have computer controlled fuel injection or direct injection, then the claims may hold true for you. But for carburetted engines and especially ones being run at altitude, keep a close eye on how your engine runs on ethanol-free fuel. It's not a free lunch.
First off, if its economy/tank range you're after and you just fill up without rejetting for ethanol-free, you're going to lose fuel economy. There is no formula where your carburetted vehicle runs on E10, then on E0 without modification where you come out ahead. The reason is pure mathematics. If you have your vehicle tuned to E10 stoich, which is 14.1:1 and you add any amount of E0, which contains no oxygen, you're mixture will run richer than it did on E10 alone.
That's great if you're looking to increase power for a tank or two, but your vehicles efficiency is going to drop. That's a purely mathematical certainty. In my case running a 68/32 mix of E0/E10, mine dropped 4% from E10 alone. Both my cruise AFR and engine coolant temperatures dropped soon after setting out.
The reason has to do with the chemical makeup of E0 and E10. E0 has no oxygen in it, whereas ethanol has one oxygen atom in the ethanol molecule. Without that oxygen to maintain stoich, your AFR will drop and so too will your engine's efficiency.
When you think about it, if you've only run E10 in your vehicle and your carburetors are tuned for best efficiency, the best you can expect is an increase in power from running E0. Conversely, if your engine is tuned on E10 for best power (12.2:1 for E10), adding E0 is a lose-lose proposition for power. You're going to pay a premium on the fuel to end up losing a lot of engine power.
The good news is, you can rejet to take advantage of E0. You just have to get the stoich formula the same as computer controlled fuel injection systems do, get your bike tuned to 14.7:1 on 100% E0. Then instead of losing 4%, you may gain 2, 3, or 4% over your best range capabilities from running on E10 with an E10 tune. I gained 4% running 99% E0 after rejetting my motorcycle specifically for E0, but I had to ride 5 - 10 MPH slower than I typically do with E10 to maintain E0 stoich of 14.7:1 too. I have a UEGO wide-band sensor/gauge on my motorcycle that tells me what my AFR is with pinpoint accuracy, in case you're wondering.
The one word of caution to doing that on a carburetted vehicle however, is that by running 14.7:1, your coolant temperatures will increase over that of E10. Mine did. Why? It's because of two things. Primarily the leaner AFR will produce more heat. And two, because E0 is stoich at 14.7:1, it's going to create more heat than an equivalent mixture of E10 gasoline, which is stoich at 14.1:1, due to the flame front temperatures of gasoline v. ethanol; 100% gasoline being about 115°F/47°C higher than 100% ethanol. Something to consider during those hot Summer months.
Here's my other words of caution for those with small carb engines running at 2,000' AMSL or above. If your engine appears to run rich (black sooty exhaust pipe) on E10, putting in E0 will just make things worse. Power and performance will drop off just as they would in the earlier examples, for say your lawn mower, generator, or snow blower, simply because if it's already rich on E10 and you take away the oxygen built into E10, your mixture will be even richer; your engine will suffocate on fuel it cannot effectively oxidize. Again, that is a mathematical certainty.
The good news for you high altitude carb users is that you may not have luck rejetting your small ICE engine for altitude, but you can make one simple adjustment that will probably gain you a freebie 100 - 200 RPMs at full throttle. Increase your float-bowl float height. Doing so decreases the fuel level inside the float bowl and subsequently your AFR will be slightly leaner and more than likely more powerful.
I couldn't go as far as I thought on E0 stoich jetting now filled with a 40/60% E0/E10 mix. It took about a whole 10 miles for the engine temps to soar up near 200* F with little trouble and mixtures that floated in the 15s and 16s, before I got my first sensation of detonation upon acceleration (throttle load). Air temps were just above freezing and humidity was higher than normal for these parts, but despite that there it was, crackling away. Naturally, I backed off the throttle to reduce load and once up to higher speeds and higher RPMs I was able to manage both the engine coolant temperatures and AFR to keep it at or below E10 stoich of 14.1:1.
After returning my jetting to a much richer setting, my previous E10 fuel jetting, the bike is still running approximately 0.2 - 0.3 richer, but that'll soon change once I get this ratio out of the tank and dilute it with more E10. Engine coolant temps have mostly returned to normal again, though it's hard to tell. Temps are probably masked a little bit cooler still by the additional presence of E0.
It just goes to show that engine cylinder temperatures are more directly related to AFR than they are to E0 or E10. It will depend on how you're carburetors are jetted and for which fuel. If rich, coolant temps will be cooler. Lean, coolant temps will be warmer.
This article from 2013 states much the same as what I was able to conclude. I had not seen this until recently. Could have saved me a lot of effort, but it confirms my results. If someone tells you that you can get both better fuel economy and better power on E0, they mean on a computer control fuel injected motor, not a carbureted motor. For those of us with carburetors, it's either-or, not both; we might be able to get our jetting close to how EFI does it for better power 12.6:1 or we can tune our jetting for better efficiency 14.7:1, like EFI, but not both.
Impact of Today’s Fuels on Carbureted Engines - By Henry P. Olsen, Nov 15, 2013
Modern Gasoline and Vintage Engines
A 1997 or newer fuel injected vehicle has an ECU/PCM (computer) that should be able to make the necessary air/fuel mixture and ignition spark timing adjustments necessary for gasoline with up to a 10% ethanol mixture.
Most vehicles manufactured after 2005 should be able to handle up to 15% ethanol content in the gasoline, but older vehicles will begin to experience performance issues with the higher ethanol content in the gasoline. The vehicles that are most effected by the addition of ethanol to the gasoline are the older carburetor equipped engines which will need to have their air/fuel mixture and ignition spark advance curves retuned for these new blends of “cleaner burning” gasoline if they are expected to perform their best.
The ethanol content of gasoline will cause the air/fuel mixture of a non-computer controlled carburetor engine to shift leaner, which will often cause a loss in driveability and throttle response. These new blends of reformulated gasoline (with and without ethanol) are actually quite different from the leaded gasoline that a vintage carburetor equipped engine was designed and tuned to use...
Tuning a Vintage Engine for Modern Gasoline It’s important to understand that the modern, fuel-injected, computer-controlled engine is a very different *animal than the carbureted engines of years past. The computer of a modern, fuel-injected engine continually adjusts fuel and spark to adapt the engine to today’s ethanol and reformulated gasoline blends.
A vintage carburetor equipped engine simply cannot do this by itself, therefore you will have to retune the carburetor and distributor for these new blends of gasoline. If your customer is experiencing driveability and throttle response issues with a vintage carburetor-equipped engine the problem may be caused by the changes in today’s reformulated gasoline with the cure being to tune the ignition spark advance and air/fuel curves for the modern fuel blends of today...
Fuel System Tune-Up
The changes in the formulation of today’s gasoline most often causes a carburetor to shift about 3 to 5 percent leaner than the gasoline most carbureted engines were designed and tuned to use.
Which is another way of saying, no matter how you have your curbureted engine tuned to run on E10, it will always run richer on any additional ratio of E0 than it did on 100% E10.