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Leaky Bing Carburetors

It is very important to turn off the petcock(s) when you park your bike. This is so even if you have a late model Airhead that has the fuel-shutoff solenoid valve located on the inside of the cover over the starter motor (many have been removed, but the same caution applies). It is exceptionally important if you park your bike in a garage where there is a source of gasoline fumes ignition …such as a water heater, ETC. We do NOT need to hear about BOOOOOM! We don’t want fires, either!

Bing carburetors are commonly known to leak in several ways. The most common is fuel dumping on your boot from a grossly overflowing carburetor, typically from a side vent. Sometimes there is just a slow weeping or a slow leak from the very small hole in the bottom of the float bowl.

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Alcohol-Proof Float Kit

The MAIN advantage of these kits is that you will likely never have to replace floats. That does NOT apply to the float needles, of which there were two basic types. The VITON tipped ones have the same easy-to-lose fine wire clip as on the stock carburetors. That clip insures positive float needle operation when the needle should be leaving the needle seat and allowing fuel to flow into the bowl.

If the original floats (which DO AGE) are already really bad, and/or the float needle is already bad, things will certainly improve with PROPER installation of these PRICEY kits! Installation is, however, somewhat tricky.  IN MY OPINION, installation of these kits when the old parts were worn, often considerably, is the HONEST & TRUE reason that SOME find improvements with fuel mileage after installing the kits.

Adjustment of these dual-independent float kits is more involved than with the stock floats. These kits can cause $$$$ problems, so, please read all of this article.

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Early R75/5 Bing CV Carburetors

This article deals with problems with early versions of CV carburetors used on the R75/5. This includes getting the bike to start and to idle correctly as best possible.

A basic mini-overhaul can be done with the carburetors in place on the engine. This may be enough. Three articles, the one you are reading, and http://bmwmotorcycletech.info/bingcv.htm  ….and http://bmwmotorcycletech.info/bingcv-2.htm are not just about how to overhaul Bing CV carburetors. These articles are specifically designed to fully inform you what you need to know, as an Airhead owner/rider, about Bing CV carburetors.

While it may appear that the information in the below article does not apply to the later carburetors (except for information as to how the /9 & /10 and later carburetors are different from these /1, /2, /3 and /4), that is not so! The information in this article should be read by anyone that also works on later model CV carbs …as some things are good to know ….such as about the springs that might be added, changes in parts, and problem area.

Before working on the R75/5 carburetors to cure what might seem to be carburetor problems, such as high or irregular idle rpm or inability to properly adjust the carburetors, it is important that the engine valves be set correctly, & the ignition timing be correct. Be sure there are no vacuum leaks at the throttle shafts.  Be sure the hoses between carburetor & cylinder head are tight & not leaking vacuum (spray with any volatile solvent …must not be idle rpm changes). Never work on carburetors unless you are sure all else is OK!

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Bing CV Carburetors – Part 2

A basic MINI-overhaul can be done with the carburetors in place on the engine. This is often quite enough. Two articles, the one you are reading, AND http://bmwmotorcycletech.info/bingcv.htm are not just about how to overhaul a Bing CV carburetor. These two articles are specifically designed to fully inform you what you need to know, as an Airhead owner/rider, about these carburetors.

The one exception is if you have an R75/5, which came with a particularly troublesome version of the Bing CV carburetor. For those R75/5 carburetors, you should review the above linked articles; AND, in particular, review  http://bmwmotorcycletech.info/earlybingR75CV.htm

1. Starting problems:

It was in November of 1971 that BMW first …and almost lastly….recommended OPENING the throttle during cold or very cold starts. We all know that this can be a necessity depending on the bike, temperature (does NOT have to be very cold), & how the carburetors are adjusted. That is still true for later models, but BMW has dropped the recommendation of an opening throttle. SHAME.   While SOME Airheads will start OK with throttle shut off and enrichener turned on or fully on, many need a bit of throttle playing AS THE ENGINE BEGINS TO START.

If your Airhead starts OK, enrichener (choke) in use, ….then seems to run out of fuel, after perhaps 15-30 seconds:  
Inspect for a partially clogged jet at the bottom of the corner of the bowl well.  If OK, check the  bowl gasket and also the enrichener gasket/screws problem.  The gasket may get sucked inwards a bit, check all 4 sides; check the 4 screws too, they tend to loosen.  There is also the possibility of a wrongly assembled enrichener. If the bowl corner jets is clogged badly enough, bike might not start at all. Both situations are often much worse on cold days. Check the tube for cracks…this tube leads downwards from the carburetor body into the bowl well. Very early Bing CV carburetors have pressed-in float bowl enrichener jets, not screwed-in. THE enrichener jet in the float bowl MUST BE CLEAR, NOT CLOGGED!   Check all these items for BOTH carburetors.

WHY does the float bowl gasket make a difference in starting?  Because sealing of the float bowl is involved in how the enrichener in the body of the carburetor is able to lift the fuel from the float bowl well.

Check if you might have installed the enrichener parts backwards, or mixed-up left and right parts. NOTE that the punch prick mark on the enrichener shafts have been seen Bing-factory-installed 180° off! That is, the punch prick marks are WRONGLY DONE for the shafts of the enrichener as installed by Bing. See http://bmwmotorcycletech.info/bingcv.htm; or Part 1 of my two Bing articles on this airheads.org website.

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Bing CV Carburetors – Part 1

For a well-done overhaul article…step by step…with 44 pictures….see BMWMOA magazine, BMW-ON (BMW Owners News), March 2003, for an article in great depth by Gary L. Smith. You can probably get that back issue at http://www.bmwmoa.org. From that main page, click on left side for Country Store, and then on the Country Store page, go to Back Issues.

I have SOME nitpicking on that article:
1. See my notes in the article you are reading.
2. Use faint amount of silicone grease on all O-rings & on enrichener parts (do NOT overdo this, you do NOT want to plug jet holes).
3. If doing a complete overhaul, which involves removing the butterfly to replace the throttle shaft O-ring (be sure to silicone grease that one & be SURE to MARK the butterfly for correct refitting: something like TOP, OUTER; or TOP, facing REAR…or something of that sort….BEFORE you remove the old one. HOPE that the previous workman did not install yours backwards, because it can be fun to figure out unless you know what it is supposed to look like. In the article you are now reading I have photos of what it IS supposed to look like….. & NOT look like.
4. The article you are reading, below, has considerably more complete information about orienting the enrichener parts.

A basic MINI-overhaul can be done with the carburetors in place on the engine. This is often quite enough. Two articles, the one you are reading….and http://bmwmotorcycletech.info/bingcv-2.htm (which is article 3B) are not just about how to overhaul a Bing CV carburetor. These two articles are specifically designed to fully inform you what you need to know, as an Airhead owner/rider, about these carburetors. The one exception is if you have an R75/5, which, if stock, has a particularly troublesome version of the Bing CV carburetor, as it was the first generation of these carburetors. For these carburetors, you should review both of these above two linked articles AND, in particular, review myarticle #6:   http://bmwmotorcycletech.info/earlybingR75CV.htm

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Bing Carburetor Floats and Float Needles

Bing carburetors FLOAT NEEDLES, whether the pure slide type carburetor, or the CV type carburetor, both as used on BMW Airhead motorcycles, come in several varieties. In general, TWO present-day available versions will fit all the Airheads carburetors. Very early carburetors had a solid metal needle. That needle was available in more than one ‘style’, but for all, there was NO rubber tip nor a Viton tip, tip was simply part of the float needle. The later type of needle, that most of Airhead owners have, is similar to the photograph below. The needle shown in this photograph has a spring loaded plunger with a hole in it, with the easy-to-lose wire clip, and RED tip material. GRAY-BLACK tipped material will also be seen. I suggest purchasing the stock type needles from your BMW parts supplier, and not Bing themselves.

The all-metal needle used on early models is a different size, and will not properly fit later carburetors, and, vice-versa. Be sure to get the correct needle. If you want to install a Viton-tipped needle in a carburetor that used the Bing all-metal needle, you can, per Bud Provin (TheNickwackettGarage.com), who says to use the very common float needle used on many old Amal carburetors, as used on old British bikes. The part can be found on a simple internet search, for float needle 622/197; or, as 013, 622/197.

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R100GS Bing Needle & Jet Replacement

Sooner or later you’re going to run into someone who will insist that the needles and needle jets in your Bing constant velocity carburetors are shot, at mileages somewhere north of 30,000. The story is that the needle rubs on the needle jet and they wear each other out. I’d been noticing a drop off in mileage (to around 34 mpg on the highway) and decided, at almost 50,000 miles, to take that advice. The work took me about an hour and didn’t take any special tools. I started by turning off the fuel and dropping the float bowls. I’d upgraded to alcohol proof floats a year or so ago, along with alcohol proof lines. That meant there weren’t any problems getting the bowl loose, and there wasn’t much sediment in the bowl itself.

As you can see, there’s a big difference in the way the new floats work. So much difference, in fact, that the kit includes a new float bowl, new float needle and keeper in addition to the floats themselves (pictured at left).

The bottom of the carb (top of page) is modified as well, with a new set of lever arms to engage the pins on the side of the floats.

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