Boxerworks.com

Am just wondering if the float needle valve has been replaced along with the new float's, in reality they should be as a worn float seal will alter things.

I suppose if the float needle is visibly worn then it will affect the fuel level slightly even if it doesn't leak. The fact that they are spring loaded will reduce the amount of pressure that the floats can exert on the needle and tend to keep it seated so perhaps that limits wear. Mine still look good and they are at least 19 years old.

The slide carb needle pictured earlier in these thread looks to be solid with no rubber tip to wear and no spring loading.

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barryh wrote: ↑Sun Mar 24, 2024 5:14 am

SteveD wrote: ↑Sat Mar 23, 2024 8:06 pm Screenshot 2024-03-24 at 11-01-30 Bing Carburetor floats on BMW Airhead Motorcycles.pngSnowbum says new floats on all Bings are 10gm.

He also says 13.5gm is likely "maximum allowable". Ongoing adjustment might extend their usefulness, they'll need replacing eventually.

https://bmwmotorcycletech.info/bing-floats.htm

I hesitate to disagree with Snowbum but that's not been my experience at all.

It was my understanding that some floats were at one time 10 grams but that is no longer the case.

I weighed new floats supplied by Motobins with a certified lab scale and they weighed 12.495 grams. My experience before replacing the old floats was they will function perfectly well at 13.5 grams or more provided you lower the adjustment by 1mm per extra gram. By 14.5 grams you should be replacing them. The one old float that became a sinker and caused flooding was more like 16 grams.

It seems very unlikely to me that floats available today would weigh exactly the same as they did 45 years ago so I'm not surprised to see some difference but 25% heavier doesn't seem right.

The only realistic way forward is for people to weigh new floats when they get them which establishes a benchmark for future reference.

Great response. Some of the 'bums info might be dated by now and adding exact real world weights at purchase adds well to the info...

Not to throw a wrench into the discussion I have so-called ethanol resistant floats, two per bowl (see image). The float bowl is black so aftermarket. I took the bowl off and and measured 21mm of fuel WITH the floats in the bowl. The bowl with the floats was nearly filled to the top. Does anyone have experience with this system? If so, does this sound about right for fuel level?

Kevin

My bike runs rich thought the range. I weighed the floats and they both seem to be around 12.5 (ISH) gms on cheapy electronic kitchen scales. I put a clear float bowl on with the carbs fitted and the levels are a couple of mm below the gasket face on the forward (lower) edge of the float bowl.

Does anybody have any comparison to that? As they are both the same I am loath to start bending float tags yet.

That level seems about right to me... the exact level isn't as critical as many people would like to think. I feel you should be looking for another issue.

Forgive me if you've already given this information... it's a long thread now... how do you know that the engine runs 'rich throughout the range'?. Is this the result of empiric testing or a belief based on seat of the pants experience.

Why do I ask? A carburettor relies on a number of circuits to produce a mixture that varies to match running conditions. All of these systems overlap at various throttle and load settings to give an almost infinite number of variations. This is particularly true of CV carbs where even some of the physical settings of the carb are not under the control of the driver but determened by engine speed and load as well. As far as I know, the only way to get a definitive picture of what is happening at all speeds and load ranges is to use a dynamometer and emmissions analyser on a rolling road... and even that doesn't take account of temperature and humidity variations unless the tests are repeated.

Even fuel level in the fuel doesn't affect all of the circuits the same way.

Anyway, enough... my point is that, assuming the engine is rich under all speed and load conditions may be clouding your judgement when it comes to trouble shooting.

Rob

Rob Frankham wrote: ↑Wed Apr 03, 2024 5:59 am ... the exact level isn't as critical as many people would like to think.

+1.
Just had to chime in here. The fuel(float) level has to be within the range between too high (overflowing when parked) and too low (starving for fuel at full throttle in top gear). Picture what's actually happening in the float bowl when you lean right or left in a curve, accelerate, brake, go uphill or downhill, or ride on a washboard or pot-holed road. Then factor in engine vibration. In this specific application, Bernoulli's principle has no effect on the mixture. The well intentioned albeit misguided people on this thread that believe floats must be set with surgical precision and directly affect the mixture are basically chasing unicorns. Good luck to them. Literally millions of carb bikes are running perfectly in stock form with their float levels set within the acceptable 'ballpark' without modified floats, add-on level viewing tubes and clear float bowls. K.I.S.S

It does take more differential pressure in the carb throat to lift fuel from a low volume position in the bowl. Thus, it might lean the mixture out somewhat in that case.

Kurt

Kurt in S.A. wrote: ↑Wed Apr 03, 2024 12:23 pm ....to lift fuel from a low volume position in the bowl.

You're missing my point. At this point there is no 'low volume position'.

Half fill a small clear jar with gas.
Tilt it to all extreme bike angles while violently shaking it.
Add g-forces in every direction.
Mimic the absolute worse road (or off-road) you can imagine.
That's the actual real-life 'low volume position' your jets are working with.