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Old 06-30-2010, 04:27 PM   #1
coppertop OP
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Joined: Sep 2006
Location: Tulsa, OK
Oddometer: 244
Airhead Bing CV carb question!

My left carb was pissing gas all over my boot all of a sudden on my commute home. It looked like it was spewing from between the riveted-on plastic cover and the carburetor body. Anybody know what gasket or O-ring or what gave way? (1982 BMW R100S, 40mm CV Bing carbs, 63,000 miles, give or take...)

It might just be time for a full-on carb rebuild. It's been years since the last problem (sinking floats) and even more years since the previous problem (hole in a diaphragm).

TIA,
Grant
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Old 06-30-2010, 05:20 PM   #2
Wirespokes
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Just because it spews gas on your boot doesn't necessarily mean a rebuild is in order.

Unless the carb body is cracked there's no way for gas to come out of the name plate on the side. There is a vent hole nearby though, that could be the source. But for it to come out there would require the overflow tube in the float bowl be plugged. But I don't understand how the fuel could get that backed up to rise up and out of that vent!

So check the overflow tube, and then the reason for flooding - junk from the gas tank and if not that, a bad float valve. They get a ring around the rubber seal and don't seal that well anymore, or hang up. Another problem I've run into is a groove wearing into the float tang where it contacts the float valve and then hangs up.
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Old 06-30-2010, 06:39 PM   #3
coppertop OP
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True.

I mentioned rebuild because of the years/mileage. I was searching the technical articles at Snowbum's site before I posted and saw that he recommended carb rebuilds at around 60,000 miles.

Yes, I see the little vent hole. That must have been where it was coming from. I will drop the float bowl and check the overflow tube, and the float valve, seat and the little tang on the floats. I do have filters in line between the petcock and the carb, so I'm not sure how anything could get from the tank to the float bowl to foul the overflow tube, but stranger things have happened.

Thanks!
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Old 07-01-2010, 09:00 AM   #4
Wirespokes
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If the filter is doing its job, then crud isn't the problem. But still the general idea is to discover why the fuel flow into the float bowl isn't being turned off. It's the float valve's job to limit the height of fuel in the bowl, so it's screwing up somehow - otherwise the level would never get so high it could exit that vent!
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Old 07-01-2010, 11:54 AM   #5
Gimmeslack
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I have petcock screens, i have inline filter. A couple of months ago, one carb pissed on my boot. Looking at float-bowl, it had significant, very fine debris. I chucked it, jiggled the float/jet to dislodge whatever had kept it open, and went back to the business of riding. No problems since.

I think I'll start replacing in-line filters every season
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