bewildering Carb Problem

[sterob]

95 R80
Its fixed, but I still cannot really explain why this occured.

Had the carbs vapour blasted and I reassembled them. Tweeked the fuel levels by gently bending tab on the floats with carbs inverted.No Problem.
Refitted carbs and RHS carb's fuel bowl will not fill with fuel.....
Took the bowl off...floats hanging down. Still no fuel. Removed fuel line from carb and fuel pisses out. Refit fuel line to carb, still not fuel.
Remove float...needle still attached to float with wire clip....needle not jammed up against seat.( could see if moving with the float. )
Blow through fuel port on carb with compressed air. Clear. Refit fuel line ( still with bowl off ) still no flow....
Had bowl on and off a few times ( though it was hanging the floats up....not different. Tried to swap bowls...no dice, they are 'sided'.
Started to swear profusely....

Removed float ( again! ) inspected. Could not see any reason for problem, except floats were 'slightly' misaligned.....replace. no flow....
I found a NEW set of floats in my spares....compared them side by side. Could not see any marked difference, except fuel level tang was not set yet.( as expected )
Fitted NEW floats anyway!, set the float heigh as before, refited Carb to the bike with fuel bowl off and connected fuel line. I have fuel flow!
Replaced bowl...Still have fuel flow. Bike starts normally.....

It must have been something to do with the original float but buggered if I know why or how......very annoying!!!!
Never had such a problem before. I had leaking carbs,butterfly refitted wrong, idle jets blocked, fuel bowl jets blocked,fuel level too low or too high, but not this.....grrrrr


I am better now.....

 

[pauls1150]

1) Perhaps a burr on the shaft that the floats pivot on, or a distortion inside the curled-over section that wraps around that shaft ... if I recall correctly (and maybe I don't), these shafts are directional, in that one end is serrated (for capture in the housing) and the other is not

2) float needle or clip getting cocked sideways a little (adjustment tang must be smooth & flat)

3) The floats were injected with helium, so they couldn't drop

4) A burst of gravity from one of the major planets

 

[oldandslow]

Inverted float level setting as explained in the Bing book is only for alcohol proof floats. With carb mounted and bowl removed, let float drop. If no fuel flow, there is something blocking it. Fix it. Adjust fuel flow to shut off when bowl is parallel with the bottom edge of carb body.

 

[20774]

Snowbum also has info on measuring fuel level in each float bowl after it is allowed to fill and the petcock is shut off. To me, this seems like the best way to get the right level...you see what the actual results are.

- 32mm carbs...height of fuel is 24mm
- 40mm carbs...28mm

http://bmwmotorcycletech.info/bingcv-2.htm

 

[pglaves]

Inverted float level setting as explained in the Bing book is only for alcohol proof floats. With carb mounted and bowl removed, let float drop. If no fuel flow, there is something blocking it. Fix it. Adjust fuel flow to shut off when bowl is parallel with the bottom edge of carb body.

Au contrair. With carb inverted to 15 degrees from horizontal the original floats were to be as specified parallel to the carb body base. For once both Haynes and Clymer got it right. The real technique is to measure the depth of fuel in the bowl. Equal is good. Correct is better.

As for the original post there is only one answer. If as he wrote, "float hanging down" still no fuel then the needle had to be binding for whatever reason blocking the seat and allowing no fuel flow. How or why? The physics escapes me but if indeed the float was not holding the needle up and still no fuel flowed when it would from the hose it is a very short distance in the carb body that can be the culprit.

 

[FELAW]

no fuel

Au contrair. With carb inverted to 15 degrees from horizontal the original floats were to be as specified parallel to the carb body base. For once both Haynes and Clymer got it right. The real technique is to measure the depth of fuel in the bowl. Equal is good. Correct is better.

As for the original post there is only one answer. If as he wrote, "float hanging down" still no fuel then the needle had to be binding for whatever reason blocking the seat and allowing no fuel flow. How or why? The physics escapes me but if indeed the float was not holding the needle up and still no fuel flowed when it would from the hose it is a very short distance in the carb body that can be the culprit.

Paul:
100% correct (as usual) on the float adjustment.
On the no flow problem, it seems to me that if there was no flow when the bowl was off and the float, and he said, needle hanging down then the problem isn't in the float/needle assembly, it has to be in the fuel inlet before the seat. Sounds like a one off problem like a piece of dirt in the fuel?

 

[20774]

I'd have to read back through the previous posts, but could an explanation be that a vacuum built up in the tank preventing the flow? Maybe not likely, but a vacuum problem can create lack of flow while riding along and cracking the gas cap can resume flow again.

 

[guenner]

Did you compare the weight of the old/new floats?

/Guenther

 

[pauls1150]

Just reviewed my old Bing manual... saw NOTHING in there about any difference between the float levels for alcohol-proof versus old gas type floats (except for /2 carbs which have a different setup anyway). And why would it? The purpose of that system is to fill the bowls and then stop at the desired height.

However, there were statements about making sure the shaft is straight and not dinged or scarred (and yes one end is serrated), and that the "wrap-around" hand of the float is true, round, and clear. There was also a line about the needle getting hung up in its bore... all of which support my items 1 & 2 earlier.

The weight question is interesting, but wasn't the issue actually the reverse of what a gas-soaked float would cause? And I don't see a "too light" float as an issue if the height tang is properly set anyway.

Probably all moot since Sterob got it done, but still curious...

 

[happy wanderer]

Just reviewed my old Bing manual... saw NOTHING in there about any difference between the float levels for alcohol-proof versus old gas type floats (except for /2 carbs which have a different setup anyway). And why would it? The purpose of that system is to fill the bowls and then stop at the desired height.

However, there were statements about making sure the shaft is straight and not dinged or scarred (and yes one end is serrated), and that the "wrap-around" hand of the float is true, round, and clear. There was also a line about the needle getting hung up in its bore... all of which support my items 1 & 2 earlier.

The weight question is interesting, but wasn't the issue actually the reverse of what a gas-soaked float would cause? And I don't see a "too light" float as an issue if the height tang is properly set anyway.

Probably all moot since Sterob got it done, but still curious...

Huh?? I just read it. It is all there on Page 7 under Fuel Level in the Bing Agency Manual. See Figure 7. I'd post it here but it's copyrighted.

 

[sterob]

1)

4) A burst of gravity from one of the major planets

Now THAT is something I didn't think of....lol

 

[sterob]

I'd have to read back through the previous posts, but could an explanation be that a vacuum built up in the tank preventing the flow? Maybe not likely, but a vacuum problem can create lack of flow while riding along and cracking the gas cap can resume flow again.

No, fuel flowed freely as soon as I removed the fuel line from the carb,......
I must have missed something....

 

[sterob]

Did you compare the weight of the old/new floats?

/Guenther

No...thought about it but could not find my scales and was just happy I was though to the light.