“”My Bing rebuild kit arrived and I am having trouble removing the old slide needles from my 83 R100RT. Any advice on this and other Bing carb rebuild tips?””

There are two basic types of needle mountings. One type uses a captive hidden clip, and the other type has a screw that has to be loosened.

If you have to, use a pair of pliers and protect the needles with something like thin leather at the pliers jaws. BUT you might be able to remove the needles with clean and dry fingers or try soft thin leather gloves or kitchen plastic gloves. ROTATE the needle 90 degrees as you pull slightly downward, then repeat, until needle is removed. When replacing the needles, the same 90 degree rotation, with small upward pressure, is needed for each notch of needle adjustment/replacement. When done replacing the needles to what you think is the ‘correct notch’, be SURE the needles stick out of the bottom of the slides exactly the same amount…use a vernier caliper.    I like to record that value. Mention of needle position is very commonly done by ‘notch’ number. The uppermost notch on the needle is

#1, and as the needle is adjusted to be higher and higher in the slide, the numbers increase, per notch, to #4.

 

Some needles, probably from about 1985,  were made out of aluminum and the needle grooves (notches) tend to wear rather quickly. If the wear is high, that will allow the needle to be in the wrong position vertically; it can move up and down a LOT. All needles, aluminum or steel, will also wear on their sides, as does the associated needle jet.    The needles are purposely free to move a bit angularly sideways, so normal vibration wears them, and their associated jet. Always replace needle and jet together when overhauling.

It is best to install the diaphragm/needle/slide assembly as the LAST item of a rebuild, although it can be done before the central jet parts are installed if one CAREFULLY wiggles the needle in the carburetor throat to be sure it is not getting hung up AS the central jet assembly is installed. Best to guide the needle with your other hand, at the air cleaner side of the carburetor.  It is rare that the needle catches on the central jet assembly during installation of the central jet assembly, but has happened.  You avoid the problem if installing the slide with needle attached as well as diaphragm, as last item.  If you install the slide assembly first, if the needle should get caught as installing the central jet assembly, very bad things can happen as you tighten that central jet assembly, you can bend the needle, and you can, if using enough force, destroy the carburetor central boss area.

Install the diaphragms to the slides carefully, they have locating notches, be sure as you tighten the top of the carburetor to the carburetor body, that the notches stay where they belong in the corresponding body and top notches. Diaphragms held in by screws are self-explanatory.  If your diaphragms are held to the slide by a plastic ring, be careful not to break it…mild heat from a hair dryer WILL help soften it a bit. No hair dryer: use hot water.  Use a very small amount of antiseize compound on the top cover screw threads AND taper undersides of the screws.

Lubricate the enrichener moving parts VERY sparingly with silicone grease, and don’t fill the little enrichener disc jet holes, nor allow them to be filled by the enricheners rotation. One small drop of Loctite BLUE on each of the 4 enrichener screws, before drawing up the enrichener and gasket to the body. The enrichener gasket MUST be in good condition and properly installed, withOUT sealant.   The reason for the Loctite is that the screws tend to loosen, are hard to get to with the carburetors on the bike, and loose screws lead to gasket tendency to move inwards….if so, you will have operating problems.   If you have the enrichener apart, be advised that there is a left and right shaft, marked L and R on the ends, and parts can be installed wrongly in other ways, so be careful. Be sure the O-ring on the enrichener shaft is in good condition.   The Author’s website has a LOT of information on proper assembly of the carburetors….and photos of wrong and correct enrichener shaft installation (and of the butterfly, it must NOT BE REVERSED).  There have been some wrongly manufactured shafts, that is, they are mismarked for the dimple (punch-prick) so do check my website.   The shaft ends are marked, often poorly, L and R for left and right. Do NOT MIX UP left and right enrichener parts.  Do ONE carburetor at a time!

It is considered GOOD WORKMANSHIP to always replace any O-ring or gasket when removing parts having those items when working on the carburetors.   If you put the carburetor body into a chemical dip tank you will ruin the throttle shaft O-ring, so be sure to remove the butterfly and shaft first, and expect to renew the O-ring anyway.  Use silicone grease on that O-ring.  The butterfly orientation is critical. DO NOT install it backwards.  The screws are PEENED, and you need to grind on them some to enable removal.  Upon replacement of the screws some just install them with blue Loctite and do not peen them.  You do NOT want them to loosen and flying into the engine.  The butterfly orientation…correct…and INcorrect…will be seen in photos on the authors website.

Lightly lubricate all rubber O-rings with silicone grease before assembly. If you are trying to figure out how to slip a rubber O-ring into a groove without damaging the O-ring from threads on the part, simply put a turn of black plastic electrical tape over the threads during the O-ring installation.

NEVER overtighten jets, etc. Be cautious about using excessive force on the central jet assembly, lest you break the carburetor boss.

A 100% overhaul job involves removing the butterfly and replacing the throttle shaft O-ring. Many times the shaft O-ring is fine; if apart, replace it anyway. If not leaking at that O-ring, many folks don’t change the shaft o-rings. A test for vacuum leakage at the shaft is the same type of test used for detecting leaks at the rubber hose connection to the cylinder head, and the steel dome top insert on many models….that is, spray a volatile cleaner, or brake cleaner, at the item while the engine is idling, look for idle rpm change. Thus, this should be done before removing the carburetors from the engine, unless you plan on a total overhaul anyway.

Removing the throttle shaft and butterfly is done by grinding, very carefully, using a Dremel tool or similar, to remove the factory peening on the two butterfly screws. BEFORE you remove the butterfly, check to be sure there is a dot or other marking on it, to identify the outer top. If not, mark it yourself. The butterfly LOOKS like it is the same on both sides and all edges, but isn’t. DO NOT mess up…be sure your butterfly is marked somehow to indicate TOP, OUTER (outer means towards rear of bike).   Because yours might already be in wrong, I suggest you check my website to see what the butterfly should look like, installed.

You will NEVER EVER get the idle to be OK, and the transition from idle to off-idle be good and stable, unless the butterfly is in correctly.  Besides being in the correct direction, it must operate smoothly.

When replacing the throttle O-ring, be sure to use silicone grease, and do NOT tighten the two butterfly screws without holding the butterfly fully closed by a finger. It is important that the butterfly be positioned very exactly, with equal light seen as looking through the carburetor. I hold the butterfly closed with one finger and GENTLY start snugging the screws. I usually use a teeny drop of Loctite BLUE first on the threads, and not peen later.  Peening the new screws can be done instead of Loctite. This is also to be done very carefully …you must NOT bend the shaft, etc. That means supporting the shaft on the INSIDE of the carburetor on something, such as a piece of metal, socket, whatever. If you do not peen the new screws, you MUST use Loctite blue on the cleaned screw threads.

Inspect the jet in the corner ‘well’ of the float bowl, which feeds the enrichener.  That jet MUST be clear. There is a tiny hole in the BOTTOM underside of the STOCK bowls (that means NOT the Bing aftermarket dual independent float kit bowl), this is one of the overflows or vents.  A peened-over tiny pipe is in this hole, the pipe shows itself as inside the bowl.  This vent/tube must be clear. On a rare occasion that tube has been known to leak or weep in very teensy amounts at the bowl base, and there are several ways, including a careful use of a tapered punch, to seat it better.  Very rarely it splits inside the bowl from frozen water (or?)…info on my website.

Be sure the floats fit correctly, I have seen a few that were a bit too loose on their mounting pin…squeezable to fit better…don’t overdo this, as they are supposed to jiggle some, just not so much that they could go twist and touch something. NOTE that the float mounting pin is KNURLED at ONE end, and that end comes out first, and is replaced last. Do NOT make the mistake of hamfisted use of a pliers when installing the pin…if you break the ears off the carburetor, you likely ruined the carburetor body.

For the stock white color one piece floats, the fuel level can be checked with the carburetor ON the bike, and best done on the centerstand. Put on a plastic glove to protect you from that nasty gasoline. With the petcock on, and you squatted down at the floor, lift one float slowly upward…VERY slowly and gently as you approach where the top of the float is horizontal to the lower edge of the carburetor body…. until the gas JUST stops flowing. Notice the top of the float alignment to the body of the carb…then very slowly lower the float until a tiny bit of gas starts flowing again. At those points, which should be very close to being the same point, the top of the float should be parallel with the lower body surface of the carburetor. That is what you adjust the float hinge “TAB” for. If some small difference, I prefer to have the gas JUST start to flow at parallel, as I LOWER the float. Do NOT…NOT…push but with very light pressure on the float.   It is more difficult to determine the stopping of the gas flow, float being parallel, when lifting UPwards, than releasing DOWNwards, as most models float needles have a spring loaded lower plunger pin….so do it how I said, above.  There is an easy to loose VERY THIN WIRE wire clip there too. It fits into the vertical float needle’s teeny lower end hole and over the float bridge tab.  Easy to loose part!  Fun to install too!  Best to not remove that wire clip, but you MUST if replacing the float needle (and an overhaul INCLUDES that needle, which is a source of wet foot/boots when it ages).

Brand new white floats will always work to the correct actual fuel depth, once initially adjusted. As they age, the depth may increase, causing mixture richening. The ONLY test for that is bowl fuel level, OR floating the thing in a small glass container of gasoline to see if about 1/3 is above the fuel. Floats must not sink more than that. While USUALLY, but NOT always, a float gets heavier as it ages and thus raises the bowl level, enrichening the mixture and reducing fuel mileage, this is NOT always so, and even a careful weighing of the float assembly IS NOT the best and most reliable test!!  Floating the float asesmbly in a small glass of fuel is the best test.

IF you have Bing’s dual independent float kit there is a special float adjustment that was in your Bing instruction sheet, and while these floats do not tend to deteriorate, the float adjustment needs to be done exceptionally carefully, the bridge of brass-like material is flimsy, the legs need to be parallel, and it may take a month +- for the adjustment to settle down, therefore need readjustment once or twice, and the possibility of a maladjustment/misalignment is higher. There is NO safety overflow tube in the bowl in these kits.  A complete article on these is on my website:
https://bmwmotorcycletech.info/bingindependent.htm

Early versions of these Bing kits had plastic bowls, usually of very dark color, they tended to get microscopic cracks in the corners and weep gasoline.  Early versions were also shipped with the corner jets not installed, and therefore the bowls were NOT separate left and right types (as BMW shipped the original metal ones).   There are many hints in the above website article.

Here are more hints for the stock OR Bing independent floats kits, with a few repetitions also here for extra emphasis:

1. Don’t bend the slide needle. Best to install the slide assembly last, to avoid problems when screwing in the central jet assembly, unless you use one finger from the front and guide the needle into the associated lower jet, as it is raised into the carburetor. Do NOT overtighten that central jet assembly! NOTE the brass part that the needle lowers itself into, that is located at the top of the central jet assembly. That funny tubular shaped part sticks UP very visibly into the throat of the carburetor. Mark my words: IT STICKS UP INTO THE THROAT!! BE SURE you have the correct end of it upwards during assembly of the central jet assembly back into the carburetor, that it does stick up into the throat, and is not caught up on an angle. NOTHING need be forced on a carburetor!!! If you have the wrong end upwards, it will NOT FIT.

2. When removing the float, note that the float pin is knurled on ONE end, and THAT end comes out first, goes back in last. Under NO circumstances do ANY prying or use pliers “against the cast pillars” that the pin fits into…if you break one, you’ll likely need a new carb body. VERY pricey. Usually the pin is removed by using a very tiny punch or modified common nail….it takes very LITTLE tappety tapping to move the pin. MIND that the knurled end comes out FIRST…and the pin is always replaced so the knurled end matches the post/boss that has the knurl marks.

3. Do NOT tighten idle mixture adjustment down forcefully at any time.

4. Be sure the gas tank is cleaned out, petcock screens cleaned, ETC.   Aftermarket in-line filters below the petcock(s) are GOOD to use, if they flow enough fuel, almost all will do that. I prefer the larger Napa 7-02323, which is designed for very early Volkswagens, although a Fram 4164 is OK…just not made as well. For smaller, which I am NOT fond of, use the Napa 7-02357. Sintered filters, of many types available, are OK.

5. Cussing at the teensy weensy thin wire clip you may have at the hinge tab adjustment area of the float, and which fits into the teensy hole in the float needle, is acceptable. The purpose of that wire clip is to ensure the needle positively opens the gas inlet port at the needle, when the float level decreases.  Keep extras on hand…they tend to get ‘lost’.  It is helpful to put an large piece of old white bedsheet under a carburetor when working on it, to ‘see’ where the clip went to.  It can be exasperatingly FUN to install the clip.  I install the clip to the fuel needle on the workbench, and then install the float, clip around the tab, and the knurled pin, all at one time, into the carburetor.

6. A spray can of Berryman B-12 “carburetor and choke cleaner” (particularly the non-California formula, NO C in the part number) works really well with its wand, for cleaning carb passages. A carburetor need not be tank dipped, most of the time. I simply spray the various parts and passageways, wait 5 minutes, repeat. NASTY stuff…use outdoors, away from eyes; and have eye protection…as you spray using the spray can thin wand tubing…liquid can come out of strange places from the carb.  If your throttle shaft O-ring is OK, and butterfly is installed correctly, you MIGHT elect to NOT remove them, and it is safe to spray all passages with the Berryman.

7. If you have been seeing faint gas stains around the top dome interface to the body, they don’t mean anything as far as performance goes, BUT…you can remove the top and slide assembly and turn the carb body upside down, on a piece of fine sandpaper (220 then 360), and CAREFULLY do some equal-pressure figure eights, rotating the carburetor as you do this, so as to have done the sanding squarely…..all to flatten the surface and remove a faint amount of material. BE SURE to clean off all grit.

8.  ALWAYS TEST the dome for a possibly leaky steel insert (at the top outside, not inside the top) before installing it. If it leaks at all, you can try restaking, or using epoxy very carefully. At one time we used to use some BMW emblems, with epoxy glue, on top.  The ROUNDEL article on my website has the details.
https://bmwmotorcycletech.info/roundel.htm

FLAT top carburetors have no leakage problems, because they have no steel inserts in the top.  Some other carburetors have no steel inserts.

The Author’s website contains VASTLY more information, including how to properly assemble the enrichener parts, and much more.   MANY more hints on that site too. There are at least two articles on just the BING CV stock carbs; a separate article on the independent floats kit, and more.

https://bmwmotorcycletech.info/index.html

 snowbum ABC #1843

Copyright 2021, R. Fleischer

02/17/2021