Personally, I don't believe trying to measure the fuel levels in the bowls gives an accurate reading.

Instead, I remove the bowl, hold the float up with my finger, turn the gas on, then let the float slowly drop down until fuel just begins to flow. At that point the seam near the top of the float should be even with the bottom of the carb. If it's not, I bend the tab that pushes on the float needle and try again.

Lawrence,

I've always found that the most common method of making your floats the proper  setting is to align the mold line on the float parallel with the bottom of the carb body.  I too thought the measured depth was the way to go, but could not get the 24-28 mm measurement.

I've read that if the fuel level is not correct it could effect the fuel mixture, either too lean or too rich. See page 5&7of the Bing Carburetors manual. 

I'm not an expert on this but it's worked for me on my 81 R100RT.

good wrenching

redhorse

Posted by: @632

A well-known airhead guru has published that the correct level of fuel in the float bowl is 24mm for the 32mm Bing carburetors.  I've found that level cannot be reached.  The maximum adjustment at the float yields a fuel level in the bowl of 20mm, no more. 

The bike starts with difficulty at present, despite cleaning the carbs and replacing the parts that typically show wear at 40 K. miles. I'm not sure if the "low" fuel level is responsible for this or not. At this point, I'm doubtful that the spec. of 24mm is correct.

Ideas? 

1. And when was that info written ? It might have changed for the latest version of the floats !!?? 

There is only 1 "best way" to do this and that requires you to drill a hole in the bottom of your float bowl, affix a clear tube to the hole, and then lay the clear tube up beside the carb when the fuel is turned ON. In this way the fuel level in the tube will reach the exact same level as the fuel in the float bowl. That's something you can measure AND it's exact. However, since L & R float bowls are different, AND float bowls are currently $50 each, I highly doubt we'll get many takers ! ? 

Obviously we are talking about the fuel level. With the bowl holding the fluid AND the float immersed in the fluid, any changes in shape, any casting flash, any minor variations, any molding voids in the shape of either part (bowl or float) will change the fluid level. Therefore, physical measurements of the position of the float will never really be that accurate. So the numbers may sound far more precise, but it's pure BS.

A. The most direct way then is to simply hold the body of the carb at a slight angle so that the weight if the float FULLY closes the float valve. At that point the mold line in the float should be parallel to the float bowl surface. Not great, but the best there is under the circumstances.

B. Now here's the second part everyone forgets... Once you do the process in part A, the carb body, the float and the float needle are a Set. You cannot swap any of those 3 parts with the 3 parts from the other carb. This because any variation in needle length or machining depth of the brass float valve seat will change the distance... which changes the fluid level. 

2. Unless the engine is fully warmed, all Airheads love full choke for starting. They just do. Therefore... No choke = No start. If you encounter this situation, then the Number 1 place to start looking is in the bottom of the float bowl. This is because modern ethanol laden fuels separate when they remain static. When the 2 liquids (gasoline and ethanol) come out of solution (when they are not thoroughly mixed) the ethanol starts to attract water and then things start to get clogged up. 

If you'll look closely at the inside of the float bowl you'll see a small jet in the corner that meters the fuel being used in the fuel  enrichening circuit ("the choke") portion of the carb. Because of it's position, that jet is always submerged and is simply the first to give any signs of trouble. So the first thing to do in this situation is clean out that jet so that it can pass the needed fuel to the enrichening circuit. 

Clean this tiny hole !!

Again... No choke = No start. Since ALL the fuel used for cold starting passes through that orifice, it makes sense to check it. But that orifice COULD BE an indicator of other ethanol-induced jet blocking. So besides clearing that jet, your carbs are telling you it's also a good time to pull all the jets and have a look-see at their condition. Any blocking, any corrosion, anything but shiny bare brass MUST be replaced.

Hope this helps.

Yes, I have tried to do that fuel level (depth) checking on my 40mm carbs, and it is tricky. I think mine are supposed to be at 28mm after the bowl is removed. The measurement is from the bottom of the main jet well. The problem I had is that when you take the bowl off, the float drops and dumps unwanted additional fuel in the bowl. So, I let the bowls fill, turn off the petcocks, then I removed the OPPOSITE bowl to eliminate as much fuel as possible from the lines.  Then I removed the second bowl and measured the depth. I made a tiny dipstick with a mark at 28mm for measuring. Again, measure from the bottom of the main jet well. Or, as everyone else wisely suggests, just check that the float seam is parallel with the carb body when the fuel shuts off. 

Along with checking that enrichment circuit jet in the corner of the bowl that Richard pointed out for you, also be sure the bowl gasket is in good shape.  The gasket encircles that little enrichment fuel well in the corner of the bowl.  That needs to seal so the enrichment circuit will draw only fuel through the submerged jet.  

I've given up on measuring the level of fuel in the float bowls.  I'm reverting to the tried and true method of just eyeballing the float mold line against the alloy carburetor rim. Having made that choice, I still am puzzled at the YouTube video of the RS rebuild where the mechanic attains the magic 28 mm of fuel in his carburetors. That video smacks of quality work, so it's left me scratching my head.

@4949 I've stripped the carbs and cleaned them twice at this point. They are clean. I've replace the needles, needle jets and the o-rings, with the exception of the one on the butterfly shaft. Bowl gaskets are new too. The diaphrams passed my inspection, so I didn't renew them.  What I have not (yet) done is strip the enrichener mechanism.  Given the bike's reluctance to start, I now wonder if the previous owner had those guys apart and then reassembled them incorrectly. 

Decades of experience with the R100 engines has lead me to believe that a well-tuned engine starts readily, with little use of the enrichener circuits.  In fact, I doubt there have been more than a handful of times when I'd had to move the handle bar lever to the second detent.  (I don't ride in freezing weather.) The difficulty I'm having with this R100R is completely new, as far as my experience goes. 

Posted by: @632

Decades of experience with the R100 engines has lead me to believe that a well-tuned engine starts readily, with little use of the enrichener circuits.  In fact, I doubt there have been more than a handful of times when I'd had to move the handle bar lever to the second detent.  (I don't ride in freezing weather.) The difficulty I'm having with this R100R is completely new, as far as my experience goes. 

And the same experience with the Airhead has proven to me that whenever the engine has sat over night, even in summertime temp conditions, the enricheners are always needed. Only for the first 15 seconds, but are definitely needed. I am not looking to provoke anyone, I'm simply reporting my experience. Of course all my experience has been in the moderate temperature range and moderate 1000 ft altitude of north Georgia. Different fuels, altitudes or ambients may induce different behaviors. 

I did have one Airhead that started consistently without use of the enricherners, and it was found to be running too rich. 

It’s a matter of habit for me … flip up the side stand, flip on the fuel, flip down the enrichment lever, start. If it’s a “cold start”, that’s what happens. 

Presuming the bike runs fine once hot, it does sound like something could be amiss in the enrichment circuit. I tried (and failed) to include a link, but this snowbum article has a section devoted to enrichment parts orientation. 

bmwmotorcycletech.info/Bingcv.htm 

@4949 I'm recovering from an accident at present and pulling those carburetors down again would be unwise.  However, the enrichening mechanisms seem to be the prime culprits at this point.  I don't see any other possibilities. I bought the bike during the heat of summer.  It would reluctantly start at that time.  Once running the bike performed as it should.  It's waking it up now that is giving me fits. 

I'll do a search for the Snowbum lecture on the enrichment mechanisms. I haven't given up on the Bings yet!

The main issue with the enrichener discs is confusing LH with RH. Outwardly they are identical in physical shape and size, they differ only in the hole locations so that when they are reversed the carbs misbehave. I understand that the discs are marked Left and Right to avoid this confusion, but possibly not on all models. 

Seems to me we had a thread on the subject that had some photos. You might use the SEARCH tool at the top RH of your screen. There is also Snowbum's article with photos RIGHT HERE.

I would not give up on the Bings just yet. 

Closure!

I was able to do some work on the bike today.  I verified my suspicion that the enrichener mechanism was not installed correctly.  The right one had the disc backwards.  I didn't have time to strip the left one, but after I put the right carburetor back together the bike started.  As time and my physical condition permit, I'll check the left carburetor and then do a proper tuneup. 

Thanks to all who offered suggestions and observations.

Hey, that's great news !! Glad to hear the bike is running better, and especially that you're feeling better.