Question about The Bings

[georgesgiralt]

Hi !
I own an '82 R65. it is fitted with the symmetrical filter cover and supple springs above the slides.
The jetting is 145 for the main jet, 2,64 for the needle jet and the needle is on the 4th position.
In 1984 BMW changed the filter cap to a different one with one 'trumpet" bigger than the other.
They installed a stiffer spring above the slide and changed the jetting to 138 main jet, and put the needle in 3th position. They kept the needle jet at 2.64.
As far as I know, this modification was done to decrease fuel consumption.
I'm wondering  what effect the spring above the slide has.  And what change the stiffer  spring make ?
The local Guru says those springs belong to the garbage bin, instead of the Bing....  So I can't ask him for the difference it makes  
Thank you for your help !

[Barry]

Stronger springs would richen the mixture at least in transitory conditions.

The springs slow the rise of the pistons and cause a temporary increase in air velocity through the venturi which in turn results in a temporary rich condition or accelerator pump affect. In the mid 80's the springs where stiffened to allow leaner mid-range settings without losing acceleration response.

The effect in a steady cruise is harder to figure. They effectively make the piston assembly heavier to support by the vacuum over the diaphragm so you would think the piston and needle would reach an equilibrium in a lower position than with the weaker spring.

But I don't think it's that simple. With the engine at steady revs  imagine you were able to press down on the piston; that would increase the velocity through the venturi which would create a higher vacuum over the diaphragm pushing he piston up again until the velocity was restored to the previous value. They are called constant velocity carbs after all.   So I think the stronger spring would only make a small difference at a steady cruise.

[mrclubike]

The local Guru says those springs belong to the garbage bin, instead of the Bing....  So I can't ask him for the difference it makes  
Thank you for your help !

Are you saying they take the spring completely out

I am fighting a cutting out and surging at steady level cruse at 4000rpm when the temp is below 60F  (16c)

I am running 145 main 2.68 needle jet and needle in the 3rd notch  but now my fuel milage has gone down

I have been thinking of going to your setting 145- 2.64 -4th notch

But the bike runs great with a 145-2.66-3rd notch when temps are above 16C  49mpg

[georgesgiralt]

"Are you saying they take the spring completely out "
Yes. He has a box full of them !
The first think he does if you ride a bike in for some work is to remove them and toss them...
I asked him why and he wouldn't/couldn't explain the difference it makes.

[marcmiller001]

I have this same flat-spot above 4,000 then begins pulling above 5K really well - I assume that was normal?

The local Guru says those springs belong to the garbage bin, instead of the Bing....  So I can't ask him for the difference it makes  
Thank you for your help !

Are you saying they take the spring completely out

I am fighting a cutting out and surging at steady level cruse at 4000rpm when the temp is below 60F  (16c)

I am running 145 main 2.68 needle jet and needle in the 3rd notch  but now my fuel milage has gone down

I have been thinking of going to your setting 145- 2.64 -4th notch

But the bike runs great with a 145-2.66-3rd notch when temps are above 16C  49mpg

[Justin B.]

I wouldn't expect the spring to make much difference at cruise, either.  Often a flat spot at the mentioned RPM is diaphragm related.  Possibly a little hole or rip starting?

[montmil]

I wouldn't expect the spring to make much difference at cruise, either.  Often a flat spot at the mentioned RPM is diaphragm related.  Possibly a little hole or rip starting?

The "flat spots" that show up when the load on the engine is increased around the noted revs, as in climbing a grade and then disappear as the load is decreased, is, as Justin states, usually a failing diaphragm.

The CV Bings on these BMWs are well past thirty years old. Slide bores wear, the thin rubber diaphragms can have microscopic holes that defy inspection, internal passages clog, needle wear out brass jets, blah blah blah...

Chasing your tail, unless a total disassembly, cleaning, parts replacement and a good carb balance tune are accomplished. The Lord of the Bings requires a sacrifice. Always.

[Justin B.]

Bings are usually pretty trouble-free once set up but as Monte alludes to they can try your patience at times when one is ailing...

[Hammer65]

Get the bing manual!