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Old 02-15-2015, 08:29 AM   #1
800 OP
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1982 R 80 G/S gas mileage

My 1982 R 80 G/S only takes me 12 KM/L without passenger or load. It runs perfect and the carburators have just been serviced. Have you any idea how to improve the gas mileage? Thanks
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Old 02-15-2015, 10:08 AM   #2
JR356
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Best to post this in the airheads section of"Old's Cool"section of this site.
Thats where all the airhead experts/folks hang out.
That's about 28 mpg,seems like it should be better.

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Old 02-15-2015, 03:00 PM   #3
sunlinden
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mixture?

Try adjusting the mixture screw. It sounds like the carbs are running too rich. The screws should be on the bottom and you turn them in to lean the mixture. If I remember correctly, they should be approximately 1&1/2 to 2 turns out.
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Old 02-16-2015, 07:28 AM   #4
anderstornvig
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Helloo, I thought my G/S had great mileage until I found out the speedo was about +20 km/h off, the tacho corresponding amount. Fully loaded I get anything from 15-20 km/L but I've waited too long to get it "tuned in". It's most thirsty at highway speeds where the fifth gear is not long enough, >100 km/h or so. Like you probably, I have the 37/11 gearing in the final drive.

Sorry to spec only metric units. On that note, since I see you're danish , be aware of the difference between imperial and US gallons when reading people's mpg. It's almost never specified and it's very confusing..!
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Old 02-17-2015, 08:01 AM   #5
RGregor
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Quote:
Originally Posted by 800 View Post
My 1982 R 80 G/S only takes me 12 KM/L without passenger or load. It runs perfect and the carburators have just been serviced. Have you any idea how to improve the gas mileage? Thanks
These bikes suffer from low CR and a rich carb setup.
In a BMW related magazine there was a very interesting article on how to improve mileage with these bikes.
However, it's not only buying the correct jets and needles, as Bing does not offer many variations.
In principle the procedure was to reduce the diameter of the needle at the cylindrical part for ~1/100mm and combine that with a smaller needle jet.
And smaller mains.
I have the magazines here and could look for this article to provide accurate info.
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Old 02-17-2015, 10:10 AM   #6
800 OP
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[QUOTE
I have the magazines here and could look for this article to provide accurate info.[/QUOTE]

Thanks, that would be great!
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Old 02-17-2015, 11:18 AM   #7
RGregor
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Originally Posted by 800 View Post
Thanks, that would be great!
One question in advance. You have checked valves and ignition?
You shouldn't try to fix a problem with carbs when the reason is somewhere else.

For the problem you describe you'd have to change the needle jet / needle combo to lean the mid range. However, there's only one needle available.

As a first step you could change the needle position and set the needle deeper.

Next step would be to change the needle jet.

Can you read german?
The author of the article I mentioned provides an Excel sheet for documenting/calculating carb setup.
Unfortunately all comments are in german.
http://www.mo-web.de/downloads/vergaseroptimierung.xls

The basic idea behind the modification is to lean the jetting in the middle, but not at low or wide open throttle positions.
If you reduce the needle jet you lean at low and middle positions.

The problem seems to be that the steps between the available needle jets are too big.
So if you go down one step the engine might already run too lean and start jerking (is that the correct expression in english?).
In that case you would have to:
- determine needle diameter in the cylindrical area
- reduce needle diameter with very fine emery cloth by ~1/100mm
- polish the needle in that area.

So with a smaller needle jet you'd have the same area between needle and jet in the cylindrical part, but less , which means leaner, in the tapered part of the needle. So it affects merely the mid range.

One reason why I like Dellortos. They offer so many needle jets and needles you'll always find something suitable.
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Old 02-17-2015, 01:30 PM   #8
Warin
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This is a double thread - as this thread has been moved from another forum .. the other thread is on

http://www.advrider.com/forums/showt...3#post26177123

A standard R80G/S 1980s will get
20km/l at 80km/h ...

or 50mpg (us) at 50mph.

That is with luggage, on dirt. Standard jets, needles. May have had a Staintune exhaust.
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