From the Airheads mailing list

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 a screw that has to be loosened. The screw type is self- explanatory.

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 needles 90 degrees as you pull slightly downward, then repeat, until needle is removed. When replacing the needles, the same 90 degree rotation is needed for each notch of needle adjustment/replacement. When done replacing the needles, be SURE the two needles stick out of the bottom of the slide exactly the same amount...use a vernier caliper, etc.    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 aobut 1985,  were made out of aluminum and the grooves/clips tend to wear. If the wear is very much, that will allow the needle to be in the wrong position vertically. All needles, aluminum or steel, will wear on the sides, as does the associated needle jet. The needles are purposely free to move a bit sideways, so normal vibration wears them, and their jet.

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.

Install the diaphragms carefully, they have a locating notch, be sure as you tighten up the top, that the notch stays where it belongs in the corresponding body and top notches. Use a tad of antiseize compound on the top screw threads AND taper sides of the screws. Diaphragms held in by screws are self- explanatory. If yours are held in by a plastic ring, be careful not to break it...mild heat from a hair dryer may help soften it a bit.

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 to the body. The enrichener gasket MUST be in good condition and properly installed, withOUT sealant. 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.

It is considered GOOD WORKMANSHIP to always replace any O-ring or gasket when removing parts having those items when working on the carburetors.

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 not leaking at the 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.

Removing the throttle shaft and butterfly is almost a must, to replace that O-ring, if the carburetor was used in a boil-out tank or dipped for a period of time in a carburetor cleaner pot. IF you decide to do that, you must grind 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). 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 throat 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, the jet MUST be clear. There is a tiny hole in the BOTTOM of the STOCK bowls (that means NOT the Bing aftermarket dual independent float kit bowl), this is one of the overflows or vents; well, I mean tube,...and this vent/tube must be clear. On a rare occasion that tube has been known to leak 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.

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 using a  pliers to install the pin...if you break the ears off the carburetor, you ruined the carburetor body.

For the stock white color one piece floats, the level is 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 the top of the float being 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 the float needle has a spring loaded lower pin....so do it how I said, above.

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 beaker 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!!  The external floating in a beaker 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, and the possibility of a maladjustment/misalignment is much higher. There is NO safety overflow tube in the bowl in these kits. I have a couple of personal files on these floats and adjustments and the original engineering sales information on them....which, upon request, I can e-mail. They are SCANNED, and NOT easy to understand, due to the poor quality.    Early versions of the Bing kits had plastic bowls, they tended to get 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.

More general cautions:

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 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, use the Napa 7-02357. Sintered filters, of many types available, are not as good as the pleated paper types; but 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 IS opening the gas inlet port at the needle, when the float level decreases.

6. A spray can of Berryman B-12 "carburetor and choke cleaner" 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.

7. If you have been seeing dirty brown gas stain remnants around the top dome, you can turn the carb body upside down, on a piece of fine sandpaper (220 then 360?), and CAREFULLY do some figure eights, to flatten the surface and remove a faint amount of material. BE SURE to clean off all grit.

8. TEST the dome for a possibly leaky steel insert at 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 glue, on top.

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.

http://bmwmotorcycletech.info

snowbum #1843

12-07-2007