Lower gas mileage and engine surge


Information and questions on GL1500 Goldwings (1988-2000)
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kneabling
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Joined: Sat May 16, 2015 9:14 pm
Location: tacoma,wa
Motorcycle: 1994 GL1500 SE

Lower gas mileage and engine surge

Postby kneabling » Tue Dec 22, 2015 1:45 pm



Since the weather has cooled (45 or colder) I've noticed a drop in gas mileage( 3-4 mpg)out of my 94se. I've also noticed that at those temps when coming to a stop the engine will rev from 800 up to 1200. It does settle down somewhat if I'm at the stop for more than a minute. If it warms above that it seems like the rev stops but mileage does not improve all that much. The bike has not sat or had any major work done from this summer until now. Any ideas????



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virgilmobile
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Re: Lower gas mileage and engine surge

Postby virgilmobile » Tue Dec 22, 2015 4:11 pm

You may want to read through this posting..viewtopic.php?f=6&t=31029

It covers most all the variables.

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raven41951
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Re: Lower gas mileage and engine surge

Postby raven41951 » Tue Dec 22, 2015 7:55 pm

In addition to the post, there is one more important factor. Air density. As the temperature drops, the air becomes denser, which means that there is more oxygen in the fuel-air mixture and this leans out the mix (more oxygen molecules for the same amount of fuel=leaner fuel-air mixture). In EFI, the computer compensates for air density. In our carbureted world, no such luck. This is best represented by riding up a mountain. At the bottom there is plenty of air, above 3-4,000 feet, the air is quite a bit thinner and a drop in power/mileage. Same thing happens with temperature to a lesser, but noticeable degree.

If you are in an area where MTBA is mandated in the winter blend (like me), this also drops fuel mileage noticeably. The government now knows that the MTBA does nothing to reduce pollution (which is why they put it in), but working as they do (a fraction of the speed of molasses), it will be some time before we get cleaner, efficient gas.

Personally, I would focus on Wingadmin's advice first.

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bstig60
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Re: Lower gas mileage and engine surge

Postby bstig60 » Wed Dec 30, 2015 1:17 am

Interesting theory..... I agree that elevation will make a difference in power and fuel economy. As you increase in elevation the fuel mixture will get richer due to less available oxygen in the air resulting in less power in carburated systems. Less available air with the same amount of fuel causes the available fuel not to burn completely and resulting in a loss of power. I don't think I agree that colder air has more oxygen in it.
Bill

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WingAdmin
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Re: Lower gas mileage and engine surge

Postby WingAdmin » Wed Dec 30, 2015 2:30 pm

bstig60 wrote:Interesting theory..... I agree that elevation will make a difference in power and fuel economy. As you increase in elevation the fuel mixture will get richer due to less available oxygen in the air resulting in less power in carburated systems. Less available air with the same amount of fuel causes the available fuel not to burn completely and resulting in a loss of power. I don't think I agree that colder air has more oxygen in it.


This is a bit more than a theory, it's basic carburetor engineering.

As altitude increases, air density decreases, which enrichens mixture. Carbureted piston-engine airplanes have a mixture control that allows the pilot to adjust the mixture for exactly this reason - to lean it manually at higher altitudes.

Density is also affected by temperature - as the temperature drops, the density increases, which means more oxygen (and nitrogen, and everything else) in a given volume of air. This is why piston-engined airplanes must take temperature into account when calculating weight/balance and available power. It's common practice for light airplanes operating at high altitudes to plan their departures early in the morning when it is cool, because once the air heats up the air density decreases to a point where the engine does not make enough power to get the airplane safely off the ground.

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Michael Faircloth
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Motorcycle: 1996 Goldwing Aspencade

Re: Lower gas mileage and engine surge

Postby Michael Faircloth » Wed Dec 30, 2015 11:10 pm

Another variable could that we are now on "winter" gas mixture... which is different than the "summer" blend.

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MikeB
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Re: Lower gas mileage and engine surge

Postby MikeB » Thu Dec 31, 2015 12:17 am

Yes, I do believe that in Washington State there is a winter and summer blend of fuel. I notice that my bikes suffer from a little higher fuel usage in the winter than the summer but don't pay much attention to it.

The troubling thing I see in your post is the the 800 to 1200 rpm swing when you stop. The last time I saw that on one of my wings was indication that the carbs needed to be disassembled and cleaned because the idle circuits were gummed up. Since this is a new bike to you, I'd suspect the carbs. You may get away with running a few bottles of Seafoam or Gumout through the carbs. It may help over an extended period of time.


MikeB
Tacoma, WA, USA


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