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AtsBMW
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This is my first vintage airhead. Just purchased recently. The bike wouldn't idle and the carbs leak a lot. I rebuilt the carbs and put in new gaskets,needles, floats. The bike idles really well now and performs great, but the carbs still leak. I have tried using a mild compound on a q-tip to buff the seat. They look nice and clean and bright but still the carb leaks. The fuel is coming out of the overflow tube. The tubes are tight and the leak must be coming from the bowl being overfilled. Bing sent me new seats. They are pressed in seats. Is there anything else I should check before trying to extract the seats?

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1972 R75/5 Toaster Tank SWB
1994 R1100RS

schrader7032
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San Antonio, TX
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Do the carbs leak while the

Do the carbs leak while the engine is running, while you are going down the road? Or only at idle or with the engine off? When the engine is off the petcocks need to be off as well.

With the petcocks off and the bowls off (do one at a time), can you shut off fuel by raising the float so that the mold line of the float is parallel with the upper body of the carb? If so, then one of two things might be happening. The floats are sticking on the way up to the seat. Be sure they move freely and that the carbs are not seriously tilted towards or away from the bike. Straight up and down is the place to start. You said new floats, so asking if they float doesn't work...let's hope they do.

So, if you can shut off the flow by manually manipulating the floats, then something must be wrong with the motion of the float.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

AtsBMW
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They leak while running and

They leak while running and when the bike is not running. I always close the pet cocks. I leave the bike outside after riding to "drain" the bowls to not have the fuel smell in the garage. I will put the bowls and try to manually manipulate the float to see if the fuel can be stopped.

Are the seats a problem that others have experienced? Is the seat going bad common? My bike has 45,000 miles on it.

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1972 R75/5 Toaster Tank SWB
1994 R1100RS

schrader7032
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San Antonio, TX
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I've not heard that seats are

I've not heard that seats are a serious problem...my carb seats have 100K+ miles on them with no problems. IIRC the needle valves on my Bing carbs are rubber tipped...Bing didn't do that all the time and may have discontinued it. However, if the carbs were mistreated or subjected to water intrusion, no telling what might have happened. I would think that grinding them a bit with a mild abrasive should have cleaned them up.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

mark_weiss
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With the fuel shut off,

With the fuel shut off, remove a float bowl. Place a catch basin below the carburetor and then raise the float so that the needle lightly seats. Turn on the fuel and see if the valve leaks. Lower the float to let fuel flow, lightly raise the float and the fuel should cut off. If the valve works, you will know that your problem is that the fuel level is too high.

Did you drop your floats into some fuel to check that they float?

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qualitycycleservice.com

schrader7032
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Mark, I wondered about the

Mark, I wondered about the floats not floating. But he mentioned new floats. Do you suppose they could be bad right out of the package?

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

AtsBMW
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The new floats are not metal

The new floats are not metal and hollow. They are a type of plastic/foam. The carbs were supposedly rebuilt before I bought the bike, but the diaphragms were installed wrong. The tabs were not used and the slides were both 180 degrees off. By installing them correctly the bike idled perfectly.

Due to the above mistakes I question what else may have been buggered up. The bike was only ridden 2,600 miles in the last 10 years. The carbs were supposedly rebuilt because they were all gummed up. I wonder if some thing was forced through the seat to open them up. If so the seats could have been damaged.

I am out of town until Friday. I will check the floats and see if I can manually push the floats up to stop fuel flow.

It appears to me that if the carbs are mounted correctly, mint crooked, new bowl gasket, tight overflow tube, that the Needle and seat are the only way the cabs can overflow. Am I correct? And yes they both leak!

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1972 R75/5 Toaster Tank SWB
1994 R1100RS

AtsBMW
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Carbs stop flowing gas when I

Carbs stop flowing gas when I manually work the floats. Adjusted them and got the fuel to stop leaking when the bike was off but pet cocks open. Problem is that there was not enough gas in the bowls to run the bike. Adjusted them to allow more gas. The bike runs fine now but still leaking. The leaking is much less. Guess I'll keep adjusting the floats to see if I can find the perfect point.

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1994 R1100RS

schrader7032
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I would suggest that the

I would suggest that the perfect point is not when the carb stops leaking. The float setting and height of fuel determines the perfect point.

Generally, you should let the float bowls fill, then shut off the petcocks. Remove the float bowls and use a ruler or something you can determine the depth of the fuel in the center of the bowl. For the R75/5 Bings, that height should be 22-24mm. That's your target. If it leaks then, you have another problem to fix.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

AtsBMW
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Good input. I'll look into

Good input. I'll look into this technique soon. I appreciate the dept measurement. This is better than adjusting the floats by guess.

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1994 R1100RS

AtsBMW
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Float bowls have about 19 mm

Float bowls have about 19 mm of fuel in them. They still leak. So, im not sure where else to look. It seems to me that maybe the floats are getting hung up allowing the fuel to overflow. Since this bike is new to me and I've replaced the floats (they leaked before I replaced the floats). Here are the floats I've used. Any ideas or other places I would look.

  • img_2503.jpg
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1994 R1100RS

schrader7032
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Have you determined the exact

Have you determined the exact point from which the gas is coming out? Maybe knowing that can rule in/out some aspects of the problem.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

AtsBMW
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Yes it is coming out of the

Yes it is coming out of the drain hole at the bottom of the carb. I have filled the bowls and they are not leaking around the brass tube, thus it must be coming from the top of the tube. This would suggest that the needle is not stopping the flow. I can manually stop the flow and I have adjusted the floats to stop the flow. Thinking my floats are getting hung up inside the bowl somehow. Are the floats I'm using stock? Or are they a new type float? Baffled on this one. Bike runs and drives great. Idles perfectly just leaks. Crazy

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1972 R75/5 Toaster Tank SWB
1994 R1100RS

schrader7032
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San Antonio, TX
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Floats look stock. You

Floats look stock. You mentioned you put in new floats. You should determine if they really do float. Put then in a small container of gas. If they float about 1/3 above the fluid, then they should be good in terms of floating. According to Snowbum's website, new floats weight about 10 grams.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

brook.reams
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Some other causes for leaking

Some other causes for leaking carbs:

The petcocks don't shut off the fuel all the way when the handles are turned to the off position and the bowls overflow after awhile when the bike is parked.

If the rubber tip float needle is used with the /5 model (which used a brass tip needle) I believe there is a difference in the taper of the two float needles and the seats. That may cause leakage.

Any burr or ridge on the float needle can allow fuel to leak past the seat.

Any grit or nick in the seat can allow fuel to leak past the seat.

If there is a burr on the hinge pin, or the float hinge, it can prevent the float from coming all the way up to force the float needle to seat.

If the edge of the float hinge catches on the cast pot metal boss of the carburetor body, that keeps the float from seating.

Hope this helps.

Best.
Brook Reams.

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brook.reams
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One other crazy idea is that

One other crazy idea is that the float needles are too short, perhaps because they aren't stock. I worked on bike with parts from some other bike used for the float and the carb leaked. As I say, crazy idea.

Best.
Brook Reams.

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AtsBMW
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Tested them. They float.

Tested them. They float. I'm outa ideas. I'm going to chat with the folks at Bing. Hopefully they can help. I appreciate all of the input. I'm not letting this situation dampen my enjoyment of riding this bike!

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1972 R75/5 Toaster Tank SWB
1994 R1100RS

AtsBMW
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R75/5 Carb leaks resolved.

Carburetor leaks are fixed! Story is this is a new bike for me. Prior owner “rebuilt” the carbs. The bike wouldn’t idle and the carburetors both leaked. I rebuilt, new floats, new needle, new gaskets. No change. Took carbs apart again found the the slides were in 180 degrees wrong. Corrected the issue, bike now idles great but still leaked. Ordered new seats for the float needles. Extracted the seats, put in the new ones. Still leaks! In my messing around placed my bowls on a paper towel. They left a wet spot! Realized that the brass overflow rods were split or cracked. Bing confirmed that this happens if moisture gets in the tide and it freezes. I put used bowls on and the carburetors do not leak now.

So, if your carbs leak. Pull the bowls with fuel in them, place the corner edge of a paper towel at the weap Hole if you draw fuel you have cracked tubs thus the leak out of the bottom of the weap hole. Solution. New bowls.

Thanks again for the wisdom and advice on this forum.

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1972 R75/5 Toaster Tank SWB
1994 R1100RS

schrader7032
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Nice of you to get to the

Nice of you to get to the bottom of things! A eureka moment!!

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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