idle mixture screw tech help

Discussion in 'Airheads' started by ironjack63, Feb 22, 2013.

  1. ironjack63

    ironjack63 Adventurer

    Joined:
    Feb 9, 2013
    Oddometer:
    66
    Location:
    Texas gulf coast
    I am in desparate need of some experience. I took the second carb off of my recently acquired '81 R100RT to clean it and rebuild it like the first one. I took out the mixture screw only to see that some previous owner had broken off the slender tip of this screw and the piece is still stuck in the carb body. Anyone know how to get this broken piece out without screwing up the carb body? I really don't want to spring for a new carb for a tiny piece of brass. All advice will be greatly appreciated.
    #1
  2. chollo9

    chollo9 Screwed the Pooch

    Joined:
    Jul 7, 2003
    Oddometer:
    1,628
    Location:
    Silk Hope, NC
    Compressed air is the first thing I'd try. Then I'd try it along with come aerosol contact or carb cleaner.

    If that doesn't work, a guitar string inserted carefully through the bleed hole might push it out. I'd be really careful with this though, you don't want to get it stuck alongside the taper.
    #2
  3. Wirespokes

    Wirespokes Beemerholics Anonymous

    Joined:
    Jul 26, 2002
    Oddometer:
    8,724
    Location:
    Jackson's Bottom Oregon
    Try compressed air.

    I'd never heard of anything like this happening before - it's one of those things you'll just have to stare at it and eventually the right idea will come.

    I believe those screws are steel, not brass. Perhaps there's a small neodymium magnet that can get in close enough to draw it out. Or possibly a piece of wire could be bent or held in pliers and apply force from the throat side. Squirt carb cleaner from the back side to possibly loosen it.

    This isn't something we commonly run into, so it's going to require getting inventive and coming up with a bright idea. It'll come out, just don't start beating on it! :wink:
    #3
  4. chollo9

    chollo9 Screwed the Pooch

    Joined:
    Jul 7, 2003
    Oddometer:
    1,628
    Location:
    Silk Hope, NC
    Or you could beat on it.
    #4
  5. Kai Ju

    Kai Ju Long timer

    Joined:
    Jul 29, 2009
    Oddometer:
    2,195
    Location:
    Long Beach, California
    If he screwed it in tight enough to break it, compressed air won't do this.
    Take a right angle pic and push on the broken tip coming from the throttle bore side.
    The bleed hole is directly in front of the butterfly valve.

    [​IMG]

    This should work because the tip on the bings is rather fat compared to a Mikuni or other Japanese carbs.

    Good luck.
    #5
  6. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,364
    Location:
    Silver Spring, Md
    The needles are steel.

    I suspect that you have a dented or broken off tip but it is not in the idle passage. Use a magnifying glass and see if you can see it? Use compressed air. If there is a piece of the tip in there you may be screwed.

    Another piece of advice. If you can still use this carb and are going to buy another idles screw, buy two. Replace carb parts in pairs, as a rule. You may break this rule for really expensive parts like slides or carb bodies but if you ever get there you'll probably be looking for a used pair instead anyway.
    #6
  7. ironjack63

    ironjack63 Adventurer

    Joined:
    Feb 9, 2013
    Oddometer:
    66
    Location:
    Texas gulf coast
    The end is indeed stuck. I don't believe compress air will do anything, as I have already tried a large straight pin bent into a 90 and clamped into vice grips. This did nothing, so I am stumped. The bike has been sitting for almost 7 years, so I am guessing it was run up in their forcefully and over time the dissimilar metal corrosion has really stuck this thing in tight.
    #7
  8. Kt-88

    Kt-88 I like everything.

    Joined:
    Sep 9, 2012
    Oddometer:
    1,017
    Location:
    SLC area, Utah
    This was the case with my r90. The tip of the screw was sheared and I ended up buying a new carb body. Which ones do you have? If I have an extra it's yours.
    #8
  9. Humboldt Airhead

    Humboldt Airhead Adventurer

    Joined:
    Jul 14, 2011
    Oddometer:
    87
    Location:
    Humboldt Co. CA
    Try putting the body in boiling water then use the pic. I have done this to loosen stuck screws and worked good.
    #9
  10. _cy_

    _cy_ Long timer

    Joined:
    Sep 25, 2011
    Oddometer:
    6,505
    Location:
    Tulsa, Oklahoma
    if above is truly the case and you've tried everything. including compressed air, pushing from behind, boiling water, etc and you are ready to scrap carb.

    this is a last ditch attempt at fixing with a chance of damaging seat.

    1. locate a pin drill bit set like below
    2. use a pin vise to hold tiny drill bit
    3. use jeweler's magnifier lens hood, you must see tiny details.
    4. carefully match drill bit size to undamaged seat on sister carb.
    5. very .. very .. carefully drill out broken tip. you may want to start with a smaller size bit, then finish with matching size. depending on if you are successful at starting bit in center of broken tip.

    ... here's what to do if you screwed up seat by drilling ... carefully degrease/clean damaged seat. then apply a dab of JB's Weld or your favorite gas resistant epoxy. allow to set ... then drill new hole with correct size drill bit matched to sister carb. take extra care not to bottom adjustment screw too tight before backing out.

    good luck ... above may still not work, but it's worth a try on a carb to be scrapped. who knows... you may get lucky??

    [​IMG]
    #10
  11. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    212 degrees isn't very hot. I would use some mapp gas before I did anything drastic.
    #11
  12. ironjack63

    ironjack63 Adventurer

    Joined:
    Feb 9, 2013
    Oddometer:
    66
    Location:
    Texas gulf coast
    I have the 40mm Bing CV.
    #12
  13. ironjack63

    ironjack63 Adventurer

    Joined:
    Feb 9, 2013
    Oddometer:
    66
    Location:
    Texas gulf coast
    One more item relating to this request for help, if I should succeed and get this broken tip out, where in the world can I find a new mixture screw?
    #13
  14. Kt-88

    Kt-88 I like everything.

    Joined:
    Sep 9, 2012
    Oddometer:
    1,017
    Location:
    SLC area, Utah
    I bought mine from BMW hucky's I think.
    #14
  15. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,364
    Location:
    Silver Spring, Md
    Carb parts are carried by Airhead friendly dealers and Hucky's, http://www.bmwhucky.com/ I don't know how far away you might be from an Airhead friendly dealer but if there is a dealer near you then asking for internal carb parts would reveal their attitude towards the older bikes. Hucky's is a favorite place to get parts. You should call to order after talking to Hans on the phone and he will explain his way of dealing.

    There are many other on line parts sources. There is a Web site for the Bing people them selves. A funny thing is that we almost never order parts from them, except for a few things that nobody else has, the parts will be cheaper at a dealer's.

    Here is another great place to get parts. Ted Porter doesn't have much of an online presents but he will have the parts, http://www.beemershop.com/.

    Another great on line source, the place I get to go to personally, is Bob's, http://www.bobsbmw.com/

    All the places I have mentioned so far you should order over the phone.Their web pages may help finding the part numbers you need but I think all of these sources work best with phone orders. Most of them don't work at all by using just on line.
    One place that you can order parts on line and not have to use the phone at all is Max's BMW, http://www.maxbmwmotorcycles.com/ The Max site is a favorite for using the parts fisch as reference anytime.

    There are others.
    #15
  16. _cy_

    _cy_ Long timer

    Joined:
    Sep 25, 2011
    Oddometer:
    6,505
    Location:
    Tulsa, Oklahoma
    for obscure Bing Carb parts ... Bing USA in Kansas
    http://www.bingcarburetor.com/bmw/bmw.html

    Beware of pricing, they are the highest ... if you need normal parts like carb kits, floats, etc. go with BMW dealer. for hard to find pieces like say float seats .. odds are Bing USA has it in stock.


    <table border="0" cellpadding="0" cellspacing="0" height="573" width="620"><tbody><tr height="10"><td content="" rowspan="2" height="466" valign="top" width="458">
    The only factory authorized franchise for Bing International for North America, South America and Australia.
    We pride ourselves in customer service.
    We understand what you want. We have the parts in stock and the services available to help you with all of your BING CARBURETOR NEEDS.
    [FONT=Arial,Helvetica,Geneva,Swiss,SunSans-Regular]Ordering[/FONT]

    Call us on our toll free line 1-800-309-2464 or Fax us at 620-767-7845. We also take orders and offer technical support by email: bing@bingcarburetor.com
    [FONT=Arial,Helvetica,Geneva,Swiss,SunSans-Regular]Shipping[/FONT]

    WE SHIP WORLDWIDE
    UPS, Fed X, and US mail. Most orders ship same day.
    Bing International L.L.C.

    1704 South 525 Road, Council Grove, KS 66846

    Toll free 1-800-309-2464


    </td><td height="10" width="1">
    </td></tr><tr height="456"><td colspan="2" align="left" height="456" valign="top" width="153"> [​IMG] <map name="m_flatbingmnu_KI" id="m_flatbingmnu_KI"> <area shape="rect" coords="21,351,102,378" href="http://bingcarburetor.com/flier2" alt=""> <area shape="rect" coords="49,292,113,310" href="http://bingcarburetor.com/manual.html" alt=""> <area shape="rect" coords="39,252,101,280" href="http://bingcarburetor.com/otherproducts/otherproducts.html" alt=""> <area shape="rect" coords="13,205,94,231" href="http://bingcarburetor.com/otherproducts/otherproducts.html" alt=""> <area shape="rect" coords="9,176,91,189" href="http://bingcarburetor.com/services.html" alt=""> <area shape="rect" coords="9,129,96,157" href="http://bingcarburetor.com/otherapps.html" alt=""> <area shape="rect" coords="30,96,93,112" href="http://bingcarburetor.com/boats.html" alt=""> <area shape="rect" coords="18,64,97,80" href="http://bingcarburetor.com/offroad/offroad.html" alt=""> <area shape="rect" coords="16,34,100,50" href="http://www.procarbshop.com/aircraft.html" alt=""> <area shape="rect" coords="58,0,110,14" href="http://bingcarburetor.com/bmw/bmw.html" alt=""> </map> <map name="flatbingmnu_05b85dfc64"> </map> </td><td height="456" width="1">
    </td></tr></tbody></table>
    #16
  17. r77toy

    r77toy Been here awhile

    Joined:
    Feb 19, 2006
    Oddometer:
    541
    The acid that is used to etch circuit boards will eat the steel without hurting the aluminum.
    Available at Radio Shack.
    #17
  18. chollo9

    chollo9 Screwed the Pooch

    Joined:
    Jul 7, 2003
    Oddometer:
    1,628
    Location:
    Silk Hope, NC
    Really? If this is true (only slightly doubting, as in being cautious) then it is truly a goldmine of information to be stored away. It would be the chemical equivalent of an EDM. :thumbup
    #18
  19. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

    Joined:
    May 12, 2012
    Oddometer:
    2,409
    Location:
    VA
    Concentrated nitric acid (>80%) and sulfuric (>98%) will not attack aluminum but will attack steel. Forget about finding nitric acid. Acetic acid (vinegar) will not attack aluminum. Some hardware stores sell concentrated sulfuric acid for cleaning drains. Vinegar is available in almost every grocery store. Soaking the carburetor in vinegar is much safer than using concentrated sulfuric acid but may take many weeks to corrode the steel. If you think the carburetor body is ruined, soaking in vinegar should not hurt.

    Edit: to be safe about damaging the aluminum, just soak the carburetor in water with a bit of dish washing soap. Keep the soaking carburetor warm. The steel will eventually corrode away.
    #19
  20. _cy_

    _cy_ Long timer

    Joined:
    Sep 25, 2011
    Oddometer:
    6,505
    Location:
    Tulsa, Oklahoma
    hold it folks .. has anyone actually tested Bing carbs metals in nitric acid?

    used to work at a plating shop out of high school .. have dipped many a part in nitric, sulfuric and muriatic (hydrochloric) acids.

    high grade aluminum in nitric acid will generally not damage metal. but most aluminum used for casting have other metals like copper, etc .. nitric acid will attack those metals destroying part.

    muriatic (hydrochloric) acid was commonly used to clean/activate steel before first coat of copper or what ever was spec'd.

    sulfuric acid was used in a cooled bath to anodize aluminum. so sulfuric acid will not hurt purer aluminum, but would attack copper, etc.

    dipping copper into high grade nitric acid would instantly cause a violent reaction with nitric acid attacking copper at high rate. same for steel ... nitric acid will attack other metals but not pure aluminum.

    (wear eyeglass and have lots of water handy) when diluting acid .. NEVER add water to nitric acid ... always add acid to water
    #20