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Thread: 1982 R100 Idling question

  1. #1
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    1982 R100 Idling question

    Hi All!

    So ever since I installed new carburetors, my Idle has been pretty bad. I need to constantly throttle (3000 RPM) in order to keep it going. Eventually it warms up and I can let sit in neutral for a little bit of time but it eventually sputters and turns off when dropped lower than 1000.


    Any recommendations on how to adjust/fix?

  2. #2
    Liaison 20774's Avatar
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    New carbs? What was wrong with the others? Are these new from Bing or did you buy them from someone else? What are the carb numbers on the side? When was the last work done on them?

    That said, what have you done to synch them so they run as intended? Typically this involves warming the bike up and then 1) setting the idle mixture for same RPM each carb; 2) adjusting the idle speed for each cylinder individually; and 3) setting the cable tension just off idle (say 2000 RPM) so that each carb, running on its own, results in the same RPM.

    Are the chokes (aka enricheners) working correctly?
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Registered User 6322's Avatar
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    It may also be a valve issue. Make sure your valve clearances are correct before the carb adjustments. Are your new carbs the original Bings or something else? If originals, then as described above, adjust the idle mixtures on each side, then match the idle speeds of both sides, then cables. Do you see a difference when you turn the choke on or off? May need an adjustment there as well. When the choke lever is in the off position, make sure both carb's chokes are completely closed.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '93 K1100LT, '00 R1100RS

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    Registered User STEVENRANKIN's Avatar
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    Carbs

    Okay, not much information from the original poster.

    Kurt has a very good point as does Gary.

    Poor idle can be caused by a number of things. The steps to correct it are the basic airhead tune up; First thing to do is check valve clearance, improper gap causes rough idle. Second, check and if needed adjust your ignition timing. You have electronic ignition on your bike so you don't need to worry about messing with points. The last thing to do is mess with the carbs. A lot of people get this order of things wrong way around and cause themselves problems. On your bike the ignition is pretty bullet proof, set it and forget it unless you have a huge amount of miles on the bike ignition timing stays the same. Valves are the number one culprit for rough idle I have found. They do need to be adjusted regularly, I do mine every 10K miles. I have found carbs stay in adjustment pretty well with the only real change in operation being adjusting the cables to account for minor stretch over time of use. Yes, parts inside the carbs do wear out but not for a fairly long period of time. So, my point is, some people blame the carbs for poor idle and mess with them thinking they change settings more than they actually do.

    On the carbs, first thing you want to make absolutely sure of is that the cables are adjusted with enough free play to allow the carbs to actually be in the idle mode. So adjust carb cables. Same goes for the idle speed screw, make sure it is backed off so the carbs are in actual idle. At the same time, check and make sure the choke cables are adjusted so the chokes are really off. Only after you are sure the carbs are in fact in idle mode can you make adjustments to idle with the mixture screws. The idle mixture screws can be tightened down then backed off a certain number of turns to get a preliminary setting. After that, there is really only a small amount of movement in the screw allowed to make further adjustments. It is a fine adjustment.

    Another possibility for poor cold running is an improperly working choke system. If the chokes are on all the time or not working properly, you will never be able to adjust idle or mixture.

    Kurt asks the important questions, I am assuming a lot in my reply. Good luck, St.

  5. #5
    BMWMOA #24809 jhall's Avatar
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    The OP said the idling problems began when he installed new carbs. Hopefully he has now checked valve clearance, timing, manifold leaks, fuel delivery, etc.. But how about the, "new" carbs? I am wondering if they are correct for his bike. It may also be a good idea to inspect the carbs' innards to insure the correct jets, needle position and float level. He said the bike won't idle below 3000 till completely warmed up, that sounds like a problem with the idle circuit in the carbs. It's been awhile since I rode Airheads, just got back on one recently. But, as I recall, there isn't much complicated about the Bings.

    Then too, what happened to the old carbs? If still around, maybe reinstall them and see if the idle problem changes, for better or worse.
    Last edited by jhall; 10-23-2020 at 01:23 PM.

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    Registered User STEVENRANKIN's Avatar
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    An interesting point to be made

    One of the things I like to point out in regard to idle problems is that it is not always the carbs which are at fault and in most cases, it is the valves out of adjustment. I see this happen all the time with my two airheads, when they get close to my normal adjustment mileage, they start to run just a little bit off. The valve adjustment brings things back to normal.

    For myself, I do ten valve adjustments for possibly one carb adjustment. And most of the time the carb adjustment is a minor adjustment of cable pull off due to minor stretching of the cables.

    I understand the OP changed the carbs, I have a newer set on my RT now because after 200K miles, the butterfly valve pivots wore out and caused a vacuum leak resulting in poor idle and performance. I would love to know the OP's reasons for changing carbs?
    What kind of miles he has on his bike? Some of the maintenance history of the bike would be nice to have as well.

    I remember one person a while back posted he had problems getting his bike to idle. In his post he mentioned the bike speeding up when he moved the handlebars. It took a bit of writing between a couple of us to impart you can't adjust idle if the carbs are not in the idle portion. Newly installed carbs with the cables set too tight so they don't go into idle cannot be set for idle mixture of idle until the cables are properly adjusted.

    I guess I have written enough for now. Until I see more from the OP, there is not much more to cover. Cheers, St.

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    After installing new carbs ... it really just came down to a proper balancing.. After that things ran super smooth. I wish I knew how to balance them myself because I feel like I would need to do it again now that I installed new exhausts.

    Thanks everyone for your help!

  8. #8
    Registered User 6322's Avatar
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    Thanks for reporting back and letting folks at your issue is resolved. Good riding!
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '93 K1100LT, '00 R1100RS

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    Liaison 20774's Avatar
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    Cool beans! So new carbs...those need balancing...did you have someone else do it? Balancing is pretty straight forward. There are three ranges to balance - idle mix, idle speed, and off idle throttle cable tension. Ways of doing that range from plug shorting...it's been said this is not possible with an electronic ignition but it can be done safely...or the use of external measuring devices. These devices include something like the TwinMax which compares vacuum on each cylinder to something like a $5 water manometer. Have you checked to see if there's another Airhead-skilled member in your area? Maybe the Anonymous Book could be useful to find a sympathetic teacher.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  10. #10
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    Quote Originally Posted by 20774 View Post
    Cool beans! So new carbs...those need balancing...did you have someone else do it? Balancing is pretty straight forward. There are three ranges to balance - idle mix, idle speed, and off idle throttle cable tension. Ways of doing that range from plug shorting...it's been said this is not possible with an electronic ignition but it can be done safely...or the use of external measuring devices. These devices include something like the TwinMax which compares vacuum on each cylinder to something like a $5 water manometer. Have you checked to see if there's another Airhead-skilled member in your area? Maybe the Anonymous Book could be useful to find a sympathetic teacher.
    I had BMW of Manhattan work on it.. But I dont want to lug the bike out there for every little thing. I would love to find someone local that can come on site and do minor work. Like a mobile workshop haha. Happy to pay ofcourse. I'll check on the Anonymous Book though! If you know anyone in North Nj send em my way!

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