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Starts OK, enrichener (choke) in use, then seems to run out of fuel, after perhaps 15-30 seconds: Bad gasket at float bowl surrounding the enrichener jet well; partially clogged jet at the bottom of that well; gasket/screws problem or wrongly assembled enrichener.

Consistently hard to start: check the above. Check that the gasket at the enrichener assembly is OK. If you might have installed the enrichener parts backwards, or mixed left and right parts, check for that. Check that the slides always fully return to the bottom, if not, add, if missing, to the top dome type carbs, this spring, above the slides: 13-11-1-335-324.

2. Surging at steady 30-50 mph: The 4 screws that hold the enrichener assembly plate to the carburetor are known to loosen, and the gasket pull inwards. Early model /5 had no such gasket. Good time to disassemble the enrichener (do NOT mix up parts, especially left-to-right) and lightly lubricate things, new gasket, seal the screws with a TEENY drop of Loctite BLUE.

3. Having to synchronize the throttle cables too often? You may have old worn out cables. Do NOT oil them. They have a nylon or similar lining, use only genuine BMW cables. Good time to do that bi-yearly cleaning and re-greasing of the throttle assembly at the handlebars...and note that those gears must be lined up at the marks on their teeth during reassembly.

HINT: adjust the cable lengths at 200 - 500 rpm above the idle rpm. This is the more critical point, where the butterflies are just barely off the idle stops. Be sure you end up with a bit of cable's slack with the throttle off. Up through /6 engines can usually be idled at about 800-900 rpm. Later ones seem to do better at about 1025 pm. If you adjust at nearer sea level, use perhaps 1050 or 1100, and then the rpm will not be too low at high altitudes. These rpm values are OK for the stock single spark plug and also for the dual spark plugs conversion.

4. It is normal for the engine idle rpm to change with altitude. This can be minimized by careful adjustment of rpm and idle mixture screws.

5. NEVER try to adjust the carburetors without FIRST knowing that the ignition timing is proper, valve clearances correct. NEVER adjust the carburetors without a thorough engine warmup. Garage warmup is NOT adequate. Go for a 15 mile ride!!!

6. The old method of adjusting the float level (the original dual single piece floats) is to have the carburetor upside down. That is NOT needed.   A good method when the carburetor is on the engine is to turn the gas off, remove ONE bowl, turn gas on, and lift the float slowly and VERY gently, until the gas JUST shuts off, and the top of the float should be parallel with the bottom of the carburetor casting. DO double check this by now LOWERING the float until the gas just BARELY starts to flow. The approximate same parallelness should exits. You do this second step (or, do it as the first and only step) due to the spring loaded plunger at the lower end of some of the float needles.   In a rare case that plunger is frozen up, fix that. You can turn the gas off again, replace the bowl, turn gas on, allow bowl to fill, turn gas off, remove bowl quickly.   Measure the fuel depth from the center bottom to the fuel top, using something small...such as the tip end of a vernier caliper, or a thin, narrow, machinists steel rule.
Do your best to have the bowl sitting flat and level on its base, and estimate the best you can with #1 eyeball, as there are meniscus errors, the exact height of the fuel from the bottom.
For the 32 mm carburetors, use 24 mm fuel height.
For the 40 mm carburetors, use 28 mm fuel height.
If your find your gas level quite high, the one-piece white float unit may be bad. Information on the floats is posted in a companion article on this website, BingCV.   Yes, that was a HYPERLINK. ALSO refer to that article for information on removing/replacing the float. The stock floats last about 30K, sometimes more. ALWAYS replace the float needle at that time.

7. After a LOT of miles, perhaps 60K, the needle and needle jet and the diaphragm will need replacing. That is the time one usually cleans out the central jet assembly, using a new O-ring, and some silicone grease on it. Cautions on this work are in the companion article. AVOID dipping carburetors into commercial carburetor dip-tank solutions, that will almost for sure eat up the butterfly shaft O-ring, necessitating its replacement....which involves those peened screws....and the need for careful MARKING, and then alignment and NOT reversing!) the butterfly. Berryman B-12, the particular version called 'choke and carburetor cleaner' works quite well to clean out passageways...use three times, within 10 minutes. If you remove the butterfly shaft, DO put silicone grease on that butterfly/shaft O-ring. It will last far longer and operate far smoother. Peening new screws is not absolutely necessary, Loctite (blue) seems to work OK. Again, be SURE the butterfly is installed correctly, and do not tighten the screws unless you are finger-holding the butterfly valve against the body, to be sure it is fully seated. If you reverse the butterfly, it will NOT work properly near idle and off-idle.

NOTE! from about 1986, Bing was shipping a rather soft needle, and clip. These wear badly, well, fast, compared to earlier models. They usually will not last the 60K miles I mention, above.

8. It is a good idea to be very cautious about installing the needle jet assembly if the slide and needle are already in place. The atomizer must stick up into the throat (it fits only one way), and you do NOT want the needle to hang up on an edge/corner. AVOID any pressure, do NOT bend that needle! NEVER force the central jet assembly...it should NOT require excessive force with wrench or fingers, to screw it up. Silicone grease its new O-ring.

9. The more common needles mountings method are adjusted to a 'notch', by rotating the needle 90 degrees and pulling down or pushing up during that. Some needles are in by a hidden clip, some by a screw. The topmost notch on a needle is the #1 notch. Most all airhead engines will use the second notch or the third. I recommend that you check that both carburetors ACTUALLY MEASURE the same for the needles, and write the value down. Measure, with vernier calipers or similar, from base of slide to needle tip. Try to hold accuracy to .015" or so on this.

10. If your bike tends to stumble and run out of power after a good uphill climb or a higher speed run down the highway (this could happen faster with a very full tank), loosen the gas tank cap...if there is a whooshing noise and the bike runs well again after 15 seconds or so, it is the tank vent that is clogged. Similar problems with fuel flow can come from clogged in-tank or in-petcock filters, or aftermarket filters. Most petcock models (there are at least 5), if they get stiff, can be taken apart, cleaned and silicone-lubed. Earlier versions of two petcock styles had a tall screen that stuck up inside the tank, that screen used a separate reddish-brown cambric washer. Remove washer and screen and replace with the later one-piece bonded screen/washer. It not only screens particles better, but seals better. Some petcock models have a screen built into the lower outlet...remove and clean it regularly. Remove and clean and dry out the tank every year too.

NOTE: if there is clogging of the in tank screens, or external fuel screens, the bike will tend to do these same things.

11. The band clamp that holds the curved plastic intake tube that fits between the carburetor intake and the aircleaner housing should be installed with the screw portion of the clamp ON TOP...or at least not at the bottom, at the carburetor end. This will help avoid breather oil dripping on your foot. This is applicable to the /5 models, but check the plastic pipe that connects the aircleaner to the carburetor, and if it has slots at the end that fits over the carburetor inlet, then follow this advice.

12. The diaphragm has a locating tab, that lines up with the similar recess in the carburetor body. Do not allow the diaphragm to slip out of position during assembly. The slide has a couple of holes in the bottom, they face the engine. Do NOT allow the slide to get nicked. Don't leave out the spring ...if your carburetor has one...on the top of the slide assembly. NOTE: Do NOT!!!...NOT!!!!...use anything but the original Bing or BMW diaphragms!!!! See the cautions and notes in the companion article to this one:
bingcv.htm

13. Use a faint dab of anti-seize on the dome top screws...threads AND the taper under the head... before assembly. Tighten them evenly.

14. If the carburetors were being worked on off the bike, you might consider doing some figure eights on a piece of glass and with upside down 220, then 360 grit sandpaper, on the carburetor body, top portion. Just enough to clean it up, and a tad more. It will help stop those gas stains, and might solve some strange problems you had been having.

15. Except for the flat top models, the dome should be checked for "leaking knock-out plugs"; these are located at the very top. If they are leaking in the slightest, seal them. You can test for leaking by putting gasoline into the top if it is upside down. You can try carefully re-staking the plug if you want to, or just cleaning the edges carefully, perhaps with a teeny tool and teeny bit of sandpaper....and using clear epoxy or other sealant. Some folks then epoxy a nice BMW Roundel on the tops....see my hardware page for a full listing, with sizes, and one or two DO fit those small top areas.

16. Diaphragms: A link to information on earliest Triumph Spitfire.....you will have to wade through menus to the fuel system...may still operate: http://www.spitbits.com. Stromberg CD150 supposedly uses the same diaphragm (B20924??) as the Bing 32mm. For 40 mm, use CD175. See also 1970's to 1980's Volvo. Information Unconfirmed by me personally. My personal opinion is that the Stromberg diaphragms are not the same in flexibility, and are for emergency use only....and you could, if yours gets a rip or tear, simply glue it, or use a glued-piece of condom, or whatever. It is my belief that the Stromberg diaphragms vary greatly with supplier, and if too stiff, you will have LOUSY power availability, and likely an inability to rev high enough. Therefore, my advice is: Do NOT use anything but the original Bing or BMW diaphragms...except in an emergency....where it is usually preferable to use glue and a piece of condom, etc!!!
See the cautions and notes in the companion article to this one:
bingcv.htm

BMW supplies a screwdriver 71-11-1-103-086 in the on-bike tool kit. That screwdriver blade pulls out of the plastic handle, and is reversible in the handle...and thusly you have both a Phillips and a standard. The Phillips is NOT a Posi nor Reed and Prince tip. There are better choices, and stronger, but not always easy to find a screwdriver that is small, and has both Phillips and slot ends, and fits your tools bag for the on-bike kit. Some folks purchase one of the SnapOn types, with assorted hardened magnetic tips that fit inside the handle. If you have the room and budget, the Snap-On is a QUALITY tool, that NEVER wears out the tips. Be sure you have the proper size tips...many come only with a relatively narrow single blade size tip. The proper Phillips size is #2; IF you have Phillips screws...and you WILL at other places on your Airhead. HINT: BMW carb top "Phillips" screws may not really be Phillips screws, they just might look that way. They could be Phillips, OR could be 'Posi' type. The ancient aircraft tip called Reed & Prince works nicely on the Posi screws....as, of course, does the real Posi. The Posi tip is EXCELLENT for REMOVING the Phillips type, if the Phillips is very tight. Install a Phillips type with a Phillips screwdriver. If the screws are frozen, you can try a variety of ideas, see my other carb articles. This includes valve grinding compound for a better grip, a metal block underneath and an Impakt Driver, etc. Tips for interchangeable-tip type tools are available from a variety of sources, including Snap-On. YES, the Posi IS available. The only critical place on our Airheads for this type of screw is the screws used on the top of the Bing CV carburetors. Some have installed Allen head screws there. They are OK, but don't overtighten, as many of these have a very small allen and can round-out more easily. I DISLIKE Allen screws there; particularly if not the tapered type. Some carbs had common single slot screws. BMW and Bing HAVE shipped both Posi & Phillips screws......be sure that your 'screwdriver' fits them, and if needed then do obtain a Posi #2 or Reed and Prince screwdriver #2 or tip. Remove the screws one at a time, coat the threads...and taper...with antiseize....and replace the screws.....you will appreciate that hint, later on. ***NOTE!!!....BMW's red plastic-handled screwdriver that is in the BMW on-bike tool kit, the one with the reversible insert, probably Heyco Germany brand, is NOT THE CORRECT TOOL for the Posi carburetor tops!!!....this tool is, instead, a common Phillips!!

The Posi screws generally (not always) have some radiating lines to indicate they are not Phillips type.

20.   FLOAT NEEDLE SEATS:   It is rare, but once in a great while there is a need to replace a float needle SEAT.   You may hear that they are not replaceable, or that only Bing can do it. NOT SO.     Some folks have drilled them and used an EZ-Out to remove the old one.   But, these seats are rather strongly pressed into place if you try to remove them withOUT heating the carburetor.   Here is one method, you can improvise your own:
a. Tap the seat with a 7 mm x 1 mm tap.   You could use SAE taps too...with American threads.
b. Use a screw of 7 x 1 mm thread, maybe 50 mm or so long.   Use some sort of bushing, perhaps about 8+ mm in INSIDE diameter, and about 14mm or so OUTSIDE diameter.   This bushing should be around 25 mm long. NOTHING critical here except that the OD is important so the bushing fits the needle seat carburetor area, not the needle seat.   You can now use that screw and the bushing (and maybe a washer) to DRAW OUT the old needle seat.    HEATING may well help.....as I THINK the carburetor body material expands faster than the needle seat material.
c. Use heat on the carburetor body when installing the new seat....which can be carefully tapped into place with a flat tool.
d. You need not use metric taps and screws, use any screw thread you like, that fits properly.

21. Some very late model R100GS, POSSIBLY others, and probably only 40 mm (??) Euro shipped models (?), may be found with a groove in the upper area of the slide, with an O-ring at that point.   The purpose is to help eliminate a rattle these sometimes had. It isn't necessary to retrofit YOUR bike with these, unless you have a bad rattle at idle (often on right side), and dislike the rattle.

22. The 4 screws that hold the enrichener (choke) device to the side of the carburetor have a tendency to loosen, and should be checked regularly. Early models had no gaskets, later ones did. If the faces leak from a bad gasket area, or the enrichener becomes loose, your carburetor will not operate correctly. You can tighten these screws with an offset phillips screwdriver while they are on the bike. I use a very tiny droplet of BLUE Loctite on those screws when assembling a carburetor, but it is NOT a must.

Revisions:
final update and release to website 12/08/2002 5:35 p.m., PDT., includes through item #10 only.

03/04/2007: all prior updates checked; minor clarifications including #13 added, and re-released to Internet.
12/01/2007: Update entire article; rearranging and simplifying in some areas, expanding in others. Add information
on the soft needles.