Float adjustment

[Chris in Frome]

Hi all! New to the forum as I've just bought a 1979 R60/7 with a Watsonian Monza. Sorry to resurrect this old chestnut of a topic once again but I'm having trouble with running rich. I've spent many hours fine adjusting the tab on the floats (Bing 53 slider carbs). I was wondering whether anyone had considered modifying the float height adjustment method? Rather than relying on bending the tab I thought about drilling through the float plate under the tab (and remove the tab) and fixing a nut on the plate to take an adjuster screw and locknut. Not only would it make adjustment more accurate but it would also eliminate the problem with the tab being at an angle where it contacts the float needle. I don't know if I'm able to post photos yet, with being a new member, that may help my rather clumsy description!

[barryh]

Welcome Chris,

I've never heard anyone do what you have described on any of the airhead forums over the last 17 years. While it may be technically possible to fit a screw adjustment, I wonder if it's a little over the top but I do like the precision approach. I'm not familiar with the detail of those slide carbs but the CV carbs have a wire clip that loops around the tab and through the hole in the float needle pin. The idea is that when the float falls it will positively pull the float needle off it's seat. An adjustment screw would preclude the use of that clip.

Although it's not quite correctly positioned in the pic below it shows the clip I'm talking about.

Float Needle Clip.JPG (74.22 KiB) Viewed 265 times

[Chris in Frome]

Another thing, the fuel level figures that are quoted (24/28 etc), I'm guessing they apply only to the CV carbs as the main jet well on my sliders is 25.5mm deep.

[Chris in Frome]

Thanks Barry, the float needle on mine is quite different, with a spring loaded ball end. Hang on, I'll try to get a pic.....

[Chris in Frome]

20240321_163922_copy_1651x1238.jpg (540.38 KiB) Viewed 258 times

[Chris in Frome]

You can see the tab has quite an angle on it, I've now ignored any depth dimensions and am using the parallel method

[r67boxer]

Does anyone else think the alcohol in the fuel affects the float level?

Yes, especially after winter storage where separation likely occurs. I recently brought an R80 out of storage with what I thought was premium fuel - no ethanol - in the tank. Upon full acceleration it hesitated noticeably. Floats were set correctly, jets were good and spark was strong with new plugs. I drained the fuel and replaced with no ethanol fuel (coloured marine premium fed from a separate filler hose at the gas station to ensure no ethanol). It now runs without hesitation.

Kevin

[barryh]

I'm in no doubt that floats absorb fuel and become heavier. I've even noticed it with new floats that initially gain a small amount of weight.

Basically if you don't know the weight of your floats then you don't know the fuel level is set correctly short of a see through float bowl or sight tube. You can replace the floats but at £60 a pair inc. postage they are not that cheap to be doing it too often. Better to buy a cheap digital weigh scale for a fraction of that amount and check the weights before replacing them.

[SteveD]

Screenshot 2024-03-24 at 11-01-30 Bing Carburetor floats on BMW Airhead Motorcycles.png (86.31 KiB) Viewed 189 times

Snowbum 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

[barryh]

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.