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Old 07-01-2013, 12:16 PM   #14
Hookalatch OP
Born Under Bad Sign
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Joined: Feb 2006
Location: Cottonwood, CA
Oddometer: 404
Final jetting adjustments

In case anyone stumbles across this thread during a search I thought I would post my final (at least at this point) jetting changes. To recap- the engine is a converted 1984 R80 that is now basically a stock 1982 R100RS. The bike now has an S fairing and retains the stock R80RT 37/11 rear drive gearing. The 40mm Bings are stock for the 1982100RS engine.

Bing recommended 160 main jets and 35 idle jets. I am still using those jet sizes. They recommended a 2.66 needle jet and the needle in the second groove from the top. I went with a 2.68 needle jet and left the needle in the second groove. The carbs had already been converted to independent floats when I purchased and rebuilt them.

With this jetting the bike starts readily and idles fine. Acceleration was brisk and without a hiccup. Even with the lower R80 gearing the bike averaged 41-43mpg on some recent trips. The only issue was at steady throttle at about 4000rpm's the bike would occasionally stumble or surge. Felt like the first indications of needing to go on reserve. Strong headwinds or gradual inclines made the problem worse. Cracking the throttle open at these times resulted in flawless acceleration.

The way the bike is geared 4000 rpm is 60 mph and takes a very small throttle opening. I raised the needles to the 3rd notch and all surging and stumbling is gone now. This may decrease my mileage a little because most of the cruising done before was dangerously lean but the bike is running very well. I may play with decreasing the needle jet back to a 2.66 or changing the main but for now I am happy and will wait to see how the overall mileage gets affected.

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