It is not true that today's oxygenated fuels are harmful to either carburetor durability or carburetor function. Good fuels, good people, good carburetors and good vendors are being maligned over this. It's time some reason was brought to bear.
Why Oxygenated Fuel?
Alcohol and other oxygenates are added to gasoline partly because it is a cheaper route to octane, and everyone seems aware of this. But it is oxygenated fuel's secondary role. It's primary role is exhaust emissions. The U.S. government is driving oxygenated fuel, not the oil refineries; oxygenated fuel is a political/environmental thing, it is not big business driven, though in the end it has definitely helped the petroleum industry. Oxygenated fuel is in fact a kind of "work around" or stop-gap measure. With many motor vehicles in the country operating dirtier than they should, the government came up with a way to "force" such vehicles into emissions compliance by the simple expedient of oxygenating their (and everyone elses) gasoline. That is, by causing the gasoline to bring more oxygen into the combustion event, thus resulting in leanness that will reduce certain important exhaust emissions. Though obviously not the best way to make these vehicles compliant, it is nonetheless a broad-reaching solution, whose result likely is greater than other efforts might be, purely due to its scope. If you want gas, you pretty much get oxygenated gas. And oxygenated gas does not harm these older vehicles, since motor vehicles are universally designed to run a bit richer than absolutely necessary for driveability reasons. There is a margin there. As long as the vehicle is in good mechanical condition and tune. (Obviously, with much of the richness margin gone with oxy fuel, any little misadjustment or other glitch can tip the engine into a performance problem. More on that later.) The oxy project isn't an attempt to make sick vehicles less polutant, but rather to cause properly running but simply older-designed vehicles to emit polutants more on a scale with their more modern counterparts. Don't confuse these two things.
But what about those modern vehicles? Aren't they affected by oxygenated fuel? No, they're not. Fuel injected vehicles, and those just before fuel injection became widespread that have electronically controlled carburetors and ignition systems, handle oxygenated gas in such a way that it is invisible to them. We call vehicles with computer controlled intakes and ignitions Engine Management System (EMS) vehicles. The GL1500 is a great example. Even its carburetor's air bleeds are solenoid-controlled! EMS engines respond differently to oxygenated fuel than do non-EMS engines. And that is part of the plan. In an EMS engine, the computer adjusts fuel and ignition to compensate for the added oxygen, producing a zero net effect on the engine. Thus to them it is invisible. The bottom line is ethanol-enhanced fuels are made for old engines, to force them to a compliance level they wouldn't otherwise meet, while the fuels have no effect on later engines. The target of oxygenated fuel is the obsolete engine design.
Does oxygenated fuel hurt carburetor parts? Emphatically, no. Two incorrect applications of facts are probably responsible for this misconception. First is the results of the use of straight alcohol as a fuel. Folks often think in terms of plain alcohol when they think E10 or E15 alcohol enhanced gasoline. But 10 or 15 percent is not the same as 100 percent. At 100 percent alcohol, still used in some forms of racing, things are indeed pretty radical. Straight alcohol as a fuel requires very dramatic changes in jetting to work, on the order of 2.7 times as rich, without which changes carburetion would be so lean the engine would not run. Incidentally, straight alcohol is so resistant to intake's evaporative process that you can't even start an engine on it. Race bikes using alcohol are started on gasoline. Even the early 80s all-alcohol Brazil-market Honda 125 street bike had two fuel tanks, the main one alcohol and the second smaller one gasoline for starting (and cast iron engine parts). The point is, straight alky as a fuel is very radical; it's nothing like alcohol-enhanced gasoline. Sure, at 100 percent, there are indeed considerable maintenance consequences using straight alcohol as a fuel, such as severe aluminum carburetor body corrosion in a stunningly short time. It's a constant problem in racing. But alcohol-laced fuel isn't the same as straight alcohol fuel. And the long-term effects are not very similar at all. Moreover, even if the small amount of alcohol was a problem, several other oxygenates are used in oxygenated gasoline besides alcohol. Ether, for one.
The other fact about oxy fuel and carburetor parts has to do with the ubiquitous motorcycle carburetor kits out there. Sensible people just don't use them; the're junk. And one of the ways they're junk is their rubber parts, which, you guessed it, are made of a rubber compound not much sturdier than chewing gum. Squishy, is another way to say it. You can indeed expect these cheesy o-rings and gaskets to be affected by significant levels of oxygenates in gasoline. However, in over 40 years of working with carburetors, I have seldom encountered and never used these parts, amd consequently, I can count on one hand the number of times I have observed oxygenate-relelated deteriotion.
The second misunderstanding grew out of early experiences in the car world. Some car carburetor gaskets, notably and famously those in one American manufacturer's products, were affected at the outset of E10's use. However, if we limit ourselves to the major four Japanese powersports brands, the effect on the powersports market is neglible. Their carburetors have always been manufacturered to a very high standard. Some folks have reported soakng aftermarket motorcycle float bowl gaskets in E10 and observing them swell slightly. Guess what? This same result was observed in the 1970s with stock float bowl gaskets and that period's gasoline, and is why pro techs know to shrink them back down in cold soapy water should the gaskets stand in fuel for any period of time. Really. A non-issue. Do specially-made, more expensive aftermarket Viton gaskets better resist this swelling? Of course they do. Viton is a terrific material in terms of its resistance to chemicals. But this in no way implies that using stock or equivelant gaskets will result in leaks or other problems. They didn't in 1975 and they still don't today.
Well, what about performance? Many have said carburetion suffers from oxygenated fuels. This is simply not true. As mentioned previously, machines whose carburetion is not correctly adjusted or whose engine suffers in some other way will in many cases respond to oxygenated fuel with expectable performance issues. And issues that are easily adjusted out and should have been before E10 ever got near the carburetor, will often show themselves more readily with oxygenated fuel. Remember that margin. Idle mixture screw settings, for example, which Honda manuals consistently incorrectly specify for their late 1970s and early 1980s bikes. Mark this. Every legitimate tweak made to vintage carbs done in the name of oxygenated fuel is a tweak that was actually needed in that carb long before it ever rolled off the assembly line 30-40 years ago and long before there was widespread use of oxygenated fuel. These tweaks are effective not because they counter oxy fuel's effect but because they overcome deficiencies that originated on the engineer's drawing board. Honda's VB series carburetors as found on the CB/CM 400 and 450, CX500 and CX650 (and GL500/650), GL1100, early DOHC fours and the six-cylinder CBX, are good examples. All of these carbs suffer from performance glitches due to compromises made in production for which oxygenated fuel is often blamed today and which in fact are not the fault of the fuel. Back in the 70s and 80s we blamed Honda. Now everyone blames the gasoline. It has nothing to do with the gas. It's a simple fact, despite all the noise made to the contrary. The bottom line is those reporting issues with oxygenated fuel are imvariably folks with bikes that need work, not an altogether surprising thing on vehicles over 30 years old.
Oxygenated Fuel's Faster Breakdown
Finally, there is the myth that oxygenates in the fuel cause it to break down and go bad faster. It's inarguable that modern fuels break down faster. But the presence of oxygenates in this case is merely tangential. It is not the oxygenates that make the fuel break down faster but rather the lack of the ingredients that used to be in gasoline and now aren't as the result of evaporative emissions control legislation. These missing ingredients include the aromatics and other ingredients that made gasoline what it was 50 years ago. Specifically, benzene, toluene and xylene. So it's not what's in the gas but what's not in it that is the problem, when it comes to fuel storage.
There is a new kind of "alcoholism" rampant in the powersports industry. This worry in the industry, much of it generated by the American Motorcyclist Association, regarding oxygenated gasoline is itself an insidious malady that counters reason. Internet user forums continue to foster this silliness, and are probably directly responsible for the average person who does not know all the facts being so thoroughly mislead. More than this, it appears from talks I have had with government analysts, that one organization is primarily driving this issue, and that is the NMMA, the National Marine Manufacturers Assocation, whose member manufacturers, companies such as Mercury Marine, are causing all the fuss: stirring up foment, testifying before congress, and claiming their engines are at risk. Note this. In all the rhetoric, try to find substantiative examples of the damage or harm all these folks are talking about. You won't because it isn't there. I asked my government contact five times for examples, and all he could come up with were copy and pastes of and links to much of the same hand-wringing, worrying, fretting, and declarations without substance that are found in many places on the Internet. No pictures of damage. No citations of damage. No accounts of damage. None. This issue, if it is real somewhere, isn't real in the powersports industry at least (and may not be even in the marine industry), and within it, no one is alarmed or confused. Here is a fact worth noting. All of the major powersports manufacturers publish their positions on oxygenated fuels in their owner's and service manuals. None prohibit or discourage oxygenated fuel use. On the contrary, they are explicit in the naming of oxygenated fuel types and list oxygenate percentage limits that are very liberal and were in fact hammered out in meetings with government agencies. Neither are there warnings in these publications regarding possible maintenance or performance issues. None. If the motorcycle manufacturers themselves are unconcerned with the idea of oxygenated fuel use from either the durability or performance standpoint, why should you be?