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Carburetors part 10 |
Ethanol
Today’s gasoline became oxygenated as part of a passive emissions control program that forces earlier vehicles to comply with much later model emissions standards, standards they were never designed to meet. Newer vehicles aren't targeted and aren’t affected because their computerized fuel injection systems automatically adjust and the ethanol is thus “invisible” to them. The targeted, older, non-computerized vehicles on the other hand can’t adjust so lean out slightly, improving exhaust emissions. The assumption on the uneducated Internet is that this leaning necessarily harms these engines. But this isn’t so. Ethanol doesn’t hurt performance because manufacturers have always built into every vehicle a margin of over-richness for driveability at different sales destinations and as a hedge in connection with the manufacturer’s warranty. If you ever worked in a shop that had a dyno and was near a club-level roadrace track you would know about this. Every race season, production-class racebikes were jetted leaner for max power, and after the season ended richened back up again for street use. Every streetable vintage Honda has this richness margin. The manufacturers put it there for their reasons, the government slightly preempts it for theirs’.
Ethanol being evil is a fairy tale. The three claims made against it—corrosion, loss of performance, and chemical damage of rubber components—are easily disproved. First, corrosion. The idea that oxygenated gasoline corrodes carburetors started with the National Marine Manufacturers Association (NMMA). Yup. Outboards. However, marine carburetors had bimetallic construction, that is, steel float bowls bolted to low grade aluminum carb bodies—a dissimilar metals combination that was a sure recipe for electrolysis-generated corrosion, especially when combined with a life near water. You found this same bimetallic carburetor construction on some lawn mowers and portable generators back then too. But not on any Honda streetbike. But what about reports of corrosion, then? Before 1978, Honda’s carburetors were cast of a very low grade aluminum alloy heavy in zinc because this metal was easiest to manufacture. This high-zinc aluminum alloy makes pre-78 Honda carburetors very susceptible to corrosion. They have always corroded faster than other carburetors. And while ethanol gas can indeed hasten that corrosion, it is not the primary cause. No Honda roadbike carburetor is more than slightly more at risk for corrosion due to ethanol’s presence than they were when it was absent.
Second, performance issues. The aforementioned richness margin, even after being reduced slightly by ethanol, cannot legitimately be blamed for performance shortcomings. The OEMs have communicated to the feds how far they can play with the richness margin. It’s even published in the bikes’ owners manuals. There is enough margin there so the ethanolized-gas works properly in a wide variety of conditions with no drawbacks—when the engine is healthy.
And there’s the catch. The factory richness margin, once ethanolized, is of course smaller, thus closer to the tipping point. And that tipping point is reached when the bike’s maintenance is neglected. Its fuel needs are then pushed deeper into the margin, a margin shrunken by oxygenates, and performance suffers. How does that happen? Every career machanic knows that wear and neglected maintenance increases the demands on carburetion, making it effectively leaner. That is, combustion efficiency is reduced, which makes the engine use fuel wastefully, which makes the formerly adequate carburetor no longer adequate—it’s leaner in a practical sense. But this is not the gasoline's fault. It's the bike's. All over powersports media folks assume ethanol is to blame for any and all performance issues. But the reality is, ethanol gas is a concern in terms of performance only when the bike has low compression, dirty carburetors, neglected ignition components, and other maintenance shortcomings. And you can observe this truth by noting that none of the OEMs has publicly communicated concern for ethanol, and by finding that no authority on the inside of this industry thinks twice about it.
Third, the argument of supposed deterioration of rubber parts. This one is simply a misunderstanding common among folks who have little or no history in the motorcycle field. No stock or other high quality aftermarket replacement rubber parts swell or break down any more than they did back in the 60s and 70s long before ethanol fuel was common. And yes, rubber float bowl gaskets swelled back in the day, before ethanol. That’s why career mechanics kept a coffee can full of soapy water nearby. On days when I spent half to two-thirds of the day in the dyno room, I found that particularly handy when repeatedly removing ZX11 carbs off the engine and flopping them upside-down for jet changes. Every 45 minutes, more or less.
Some might argue that alcohol ravages aluminum, and this is true, it does. I have some experience with the use of straight alcohol in racing. Racing alcohol does indeed absolutely destroy aluminum carburetors. But ethanol-spec gasoline is worlds apart from straight alcohol. There isn’t enough alcohol in today’s ethanolized gas to affect the carbs in the same way as 100 percent does. The two are completely different things.
One more thing. I find it amusing that so many want to attribute the now very short shelf life of gasoline to the presence of ethanol. Nope. Another misunderstanding. It’s not what is in today’s gasoline that makes it gel in just three weeks, it’s what is missing from it. The aromatics in gasoline—the ingredients that made it smell exotic—were removed in the early 1980s for biohazard and evaporative emissions reasons, and also because fuel injection tolerates and has therefore allowed “dumber”, less refined gas to be used. It is the absense of these previously very common chemicals (one of them toluene) that today demand diligent use of a fuel preservative to prevent carburetor fuel gelling.
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Last updated January 2025 Email me © 1996-2025 Mike Nixon |