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314 Posts
Discussion Starter #1
The gas at my local stations is supposed
to contain 10% ethanol, though it actually
runs closer to 18% ethanol. My bike has
a carburetor, so it tends to run lean with
this fuel. Now that it is getting colder,
and the air is denser, it is leaner still.

As a result, I've been getting over 110
mpg. I don't mind the economy, but the
performance is really starting to suck.

I'm wondering if many others are
noticing such issues with their bikes.
 

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Premium Member
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14,680 Posts
I saw one of those 10% ethanol warnings at the pump the other day and wondered what effect it would have on the bike
 

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23,909 Posts
The maximum ethanol content can't be above 10% if it's labeled as such by law. I doubt many companies would put 18% in the tanks and risk the fines involved.
 

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I fear no beer
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459 Posts
I read that ethanol will cause gunk to build up in the fuel system faster than using gas without ethanol,not sure if it's true or not.
 

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Discussion Starter #6
By sister's husband is an auto mechanic
(and race car driver). He has a way of
testing gas for its ethanol content.

He said the are allowed to go over 10%
as long as they don't go over 20%.
Because of the subsidy on ethanol,
it is cheaper than gas, so they try to
put as much as they can into it.
 

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track junkie
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797 Posts
Try changing your jets to work with this fuel. Pilots are probably fine, but upsize your main jets 1 size.
 

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Discussion Starter #8
Try changing your jets to work with this fuel. Pilots are probably fine, but upsize your main jets 1 size.
That's what I was planning, since I doubt
there is anywhere I could find "real" gas
now. (unless you consider aviation gas
at $4.50 per gallon. Ouch)
 

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Darn Tree huggin hippies. I hate ethanol. You would think that a group so inclined to save plants would think twice before encouraging everyone to use a fuel made from them.

Ethanol sucks, it creates varnish, sucks in water, eats rubber o-rings, and runs like crap.
 

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peanuts choot choot
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704 Posts
Don't darn the tree huggers. Ethanol isn't any better for the environment. Darn the farm subsidies, and lack of rational scientific analysis of the situation. E-OH from corn is one of the most inefficient uses of our resources.
 

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Honk if you've never seen a gun fired from a bike
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But the lead can act as a lubricant as well as an octane alternative, so for some it may not be entirely bad.
 

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Sickle Punk
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aviation fuel = 100 octane low lead, not sure you want the lead in there...

at least this is what I've been told by my cousin who flies
or running 100 octane on "low compression" street bikes, that will gunk up the engine with unburnt fuel, and just might not denotate in cold weather...
 

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Gone.
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Uhm, how would you know it runs closer to 18% ethanol anyway? How are you measuring that?
That's what I was wondering. It takes a pretty specific kind of lab to analyze gasoline content, right? I know of one in Cary, NC, that does the testing for NASCAR, but I guess there could be some other sort of simple way to get a rough idea of content. Heck, I dunno.

I'd first try adjusting your idle air, or idle fuel, mix to a richer setting to see if that will have any carry-over to eliminate your lean running condition. If that doesn't give you any joy I'd do as Bad Monkey suggested and put in a larger main jet. I like to go up, or down, in increments of .004 and that seems to take care of most tuning needs.

You might also need to rejet a mid-range circuit, if you have one, and any other circuits you have that use jets or jet needles or whatever, but that depends on where your lean condition occurs (throttle position) and what sort of carburetor you have. Basicaly, you just need to tune your bike to the fuel you have available, based on it's set up and fuel delivery system.
 

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Challenged Mechanic
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I don't know if you can really call that "lean" running as a result of ethanol. Ethanol has the effect of raising the octane level. It should burn pretty much the same as other gas of the same octane. This does not mean you are not running lean, just that you may need to adjust your mixture regardless of the fuel.

I have heard from "experts" on both sides of this ethanol question. Some say it is bad for a bike some say because of modern additives, it is not. Take your pick. Todays' bikes are made to run on the stuff, so it partly depends on the age of your bike.

From experience, I have noted that, although I have not noticed degradation of the nitrile rubber components of my carb system, the ethanol does swell the rubber parts. This is a royal PIA when trying to fit the o-ring in its groove on the float chamber cover and getting it to stay there while you reinstall it. (Tip: a little grease spread into the groove before fitting the o-ring works wonders.) Also, the water in ethanol gas will separate form the ethanol when sitting causing obvious problems. If you use ethanol fuel, use it quickly and don't let the bike sit around unused with ethanol fuel sitting in it.

Concerning lead; back in the old days the valves and valve seats were not hardened and they needed the lead as upper lubricant. I have been reading about this and found that while this need for lead in old bikes is true generally, the old Hondas were different: "Honda used hardened valves and seats, so there is not a problem about running them on unleaded fuels, unlike many of the other manufacturer’s machines of the era." Vintage Honda Tuneup and Repair, William Silver. I don't know what kind of bike you have so you may or may not need leaded fuel. If it is old and of the leaded fuel era and NOT a honda, then you need some lead in your fuel. Someone suggested to me a mix of 2/3 pump gas and 1/3 AV 100LL. That should get you close to 95 octane (which is what my bike takes with a 9.5 compression ratio).

Cheers,

Mike
 

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Discussion Starter #18
The fuel mixture needed to properly burn ethanol
is different than that of pure gasoline. Gas diluted
with ethanol also doesn't burn at the same mixture.
It tends to need more fuel in the fuel/air mix to run
best, or stated differently, it runs leaner at the same
settings.

Raising the octane doesn't change this. It makes the
engine resist predetonation. Increasing the octane
doesn't change the amount of air the fuel needs to
burn.

The reason modern cars don't mind the ethanol is
because they are fuel injected. The sensors tell
the computer how it is running, and the computer
responds by shooting in more or less fuel.

The the only thing the carb "senses" is the
air passing through the venturi. As the
engine runs faster more air sucks more gas.
The jet and float level don't change "on the
fly."

If my bike had two needles on the carb, like
my farm tractor, I'd be able to tweak it for
each tank of gas if I needed to. As it is, I'm
stuck like so many folks, swapping jets
trying to find the one that works this week
or this month.

I've tried changing the idle mixture, and can
correct the low end, and make the lower
midrange better. It does affect the high end,
but not enough to really say it helps.

I'll hold the avgas as a last resort.
 
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