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Old 03-11-2004, 06:41 PM   #1
Professor Fate OP
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Question airhead poor gas milage

1983 R65. 54,000 miles. Been fighting this poor milage the last few years (35-40 mpg) It used to get 50. I just reringed it and have more power. Carbs are ballanced and have good diaphrams. Timing was adjusted up to spec. Runs good. Plugs insulator is almost white, slightly tan.
The one thing that I've noticed is gas fumes a lot coming from the tank vent. Is it possible thats where my gas milage is going. I never see it drip though. Is it time for a new gas cap or what is going on? Timing chain?
Been using an amsoil foam filter for years and may be going to a K+M.
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Old 03-11-2004, 07:32 PM   #2
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My '81 R65 never got great mileage....maybe 40-43mpg all the time. With its low gearing, it is usually just spinning so hard the fuel economy suffers. No way I ever got 50 on that bike, although my '86 R65 has done that a few times.

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Old 03-12-2004, 11:47 AM   #3
T Rex
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Did you check the needles and seats??
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Old 03-12-2004, 01:12 PM   #4
Stephen
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Just a couple of quick notes...Bing recommends new needles and needle jets every 20k miles. Perhaps a little pessimistic, but not unreasonable. At 40k, the ones on my GS were well-worn. Renewing worked wonders--I don't recall fuel consumption change, but it sure ran better.

You said "good diaphragms"...how do you know? I've replaced ones that looked good with new ones, and guess what? That's right. The new ones worked better.

Still and all, you say plugs look somewhere around okay-to-lean. Maybe your problem isn't the carbs. Still and all the more, 40 mpg is about all I ever gotten out of any bike. I've found the better I get'em runnin', the harder I run'em, so I seldom expect to improve fuel efficiency.
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Old 03-12-2004, 04:57 PM   #5
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I have not replaced the needles and jets, that may be the way to go. I took the diaphams out and looked for holes and distortion, and they looked fine, although I bought a set of them I will do them when I do the jets. I replace the gas cap seal with a fat o ring today and see if that gets rid of the fumes.
Thanks.
Fate
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Old 03-13-2004, 06:30 AM   #6
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Odds are that if the carbs are in good tune that your SPARK PLUG CAPS are shot. Check them with an ohmmeter. The caps are supposed to be 1K Ohm caps. You can replace them with NGK 5k caps and not have any problems at all. 5k is LOTS less than the 300k or more that you have now. Go to any automotive RACE shop and buy a yard of metal core spark plug cable and a pair of solder-on ends that jam into the coils. Pick up a pair of 90 degree plug caps at any bike shop. Build yourself a pair of BRAND NEW spark plug leads for less than a fifth of the cost that BMW gets.
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