Carb balancing question....

Discussion in 'Airheads' started by daveoneshot, Jan 5, 2013.

  1. daveoneshot

    daveoneshot Been here awhile

    Joined:
    Dec 14, 2010
    Oddometer:
    469
    Location:
    Vermont
    ...Details : 1978 R 100/7 with Dyna III ignition. I've heard that with these Dyna set-ups you can't just pull one plug wire off to see how fast the other cylinder is running. I used to do that on my Slash Five but I don't want to take any chances with this bike. What's the best way to isolate one cylinder to check the speed of the other one ?? Hope this makes sense, thanks in advance.
    #1
  2. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,373
    Location:
    Silver Spring, Md
    You are correct about not disconnecting a plug wire on any electronic ignition including the Dyna III. If done this way the box will die if not right away then pretty soon after. It is also not a good idea on even a /5 but a lot of riders get away with it I know.

    You need the tool listed on this page about 1/4 of the page down. Called the BMW Airhead Carb. Sync. Adapters. Either buy these or make your own.

    http://www.northwoodsairheads.com/Tools.html

    In operation the threaded rod is attached to the spark plug and the plug wire is attached to the other end. The bike will run in this fashion on both cylinders. Tighten the tool onto the plugs. It will come loose from vibration and cause the problem you were trying to avoid by using the tool. A long blade screwdriver is used to short the rod to ground, a cylinder fin, and the bike will run on the other cylinder. Instead of disconnecting a plug to keep it from firing we are now shorting the plug. Sometimes called the "shorting tool".

    When done disconnect. I have personally learned to not leave these attached to my plugs and ride around too much. They will come loose, as I have already mentioned at least once. Good Luck.
    #2
  3. SRanger331

    SRanger331 stuff

    Joined:
    Dec 10, 2011
    Oddometer:
    238
    Location:
    NW Ohio
    Like so.
    [​IMG]
    [​IMG]
    [​IMG]
    I made mine with threaded rod from Lowes and the nipples off the plugs.
    #3
  4. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    I think you would be much better off getting a vacuum take off kit from Bing and installing VTO's into your carbs and using a properly damped manometer. The best teacher on the planet to teach you how to tune by ear as long as you don't turn your ears off while you are using it!
    #4
  5. Horsehockey

    Horsehockey A GPS? Huh?

    Joined:
    Nov 17, 2010
    Oddometer:
    370
    Location:
    Vermont
    I've used the "shorting method" for years, as Disston described above. Matter of fact, Disston made the little threaded rods and nipple that I'm using now....he generously donated them to me when I lost my tool roll a couple few years ago. Like any technique, practice makes perfect.

    To get you started on your reading for the New Year, see this (it's described as "Method #2":

    http://bmwmotorcycletech.info/synchcarbs.htm
    #5
  6. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,373
    Location:
    Silver Spring, Md
    Do both. In fact buy the Harmonizer tool which is made by an inmate here and really works, I say. I never had any luck with manometers but when doing cars the standard vacuum gauge works great. On my bike it's the shorting rods and/or the Harmonizer.

    Good to hear from you HH. Been laying low I think? Hope everything is OK.

    How about those rods made by Ranger Guy? You don't think you could find some longer ones do you? LOL
    #6
  7. Horsehockey

    Horsehockey A GPS? Huh?

    Joined:
    Nov 17, 2010
    Oddometer:
    370
    Location:
    Vermont
    Things are "fine" Diss-mah-man. Thanks for asking. I've been feeling like our new airhead owner - driving himself crazy thinking that things "aren't quite right". That's the way I've been feeling about the world for some time and it's put a damper on my posting. I prefer the cocoon approach to world ennui and plan to emerge, like a cicada, in about 17 years.
    #7
  8. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,373
    Location:
    Silver Spring, Md
    We are getting old Bill. I have the same response to stuff. I hope you aren't one of those noisy type Cicadas. They were terrible around here last time. I think they'll be back in about 12 or 13 years again.
    #8
  9. Renner

    Renner combustophile

    Joined:
    Jul 11, 2007
    Oddometer:
    2,788
    Location:
    sunny SoCal
    guys... can you keep the noise down a bit?

    me: I balance by eye-ball.
    look at the slack where the cable enters the adjusting ferrule and eyeball the gap. strive for 1.5mm and keep it metric.

    if my eyes are too busy looking for other problems to resolve, or skirts, then I rest my chin on the tank and adjust for minimum vibrations.
    everybody knows this is the #2 way (whose snow-bum?) a lot of people tell me this is my best work.

    next I'll whip out my *longer* pocket shorting sticks and two long screwdrives so I can demonstrate my auditory acumen while playing a paradiddle on the fins.
    this usually dreaws a crowd even in the atacama desert.

    and if my tech day dance card hasn't filled-up by then, I'll pull my harmonizer out of my back pocket for the big-buck bling show...
    hell, I may even remove my damped $4 manometer-belt to use in parallel so those in the back can see.

    cold & wet this morning. good coffee
    I may go out to the garage and unbalance a few bikes.
    #9
  10. Bill Harris

    Bill Harris Confirmed Curmudgeon

    Joined:
    Sep 20, 2008
    Oddometer:
    9,746
    Location:
    backwoods Alabama
    Hate to raise the noise level a bit on the carb balancing mantra, but here:

    I've used everything there is, from the Eyeball through a UniSyn through Harmonisation -n my decades of doing The Balancing Act. By Ear works, but you need to have a feel for it. UniSyn works, but is crude. Manometers work but are a kludge to set up. The Harmonizer is easy to use and deadly accurate but you need vacuum fittings on the carb or intake. I added vacuum ports to my R60's slide-valve carbs and use a Harmonizer in the shop and on the road.

    But the shorting method is quick to use and reasonably accurate ( I would give it about 95%). The shorting adapters are easy to make (use an aluminum piece off of an NGK sparkplug and a couple of inches of M3 machine screw which "fits" better than a #6x32 screw).

    Main thing is to UNDERSTAND what the principles are and what you are doing and just not going through the motions. :deal

    --Bill


    PS-- good post, Renner. :lol3
    #10
  11. Renner

    Renner combustophile

    Joined:
    Jul 11, 2007
    Oddometer:
    2,788
    Location:
    sunny SoCal
    werd!

    Thas' right, man.
    and at some point the diminishing returns of 'balancing' be reached. :freaky

    -Scotto
    #11
  12. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    No luck with manometers? I am just trying to save everybody the money they spend on getting the latest electronic equivalent of a manometer every five or ten years. No luck with manometers almost has to mean it wasn't damped properly. It is very easy to damp them and adjust there damping. The harmonizer is deadly accurate? Inches of mercury, water, whatever is THE scientific standard for good reason. It's Mother Nature showing you what's going on. You can't get any more accurate. On the road? When I rarely ever sync carbs out of my shop, I just do it by ear. I can sync by ear just as good as the shorting method. The shorting method IS syncing by ear except you are matching loaded up cylinders one at a time by ear versus matching good, warm clear cylinders while they are both running in their actual running state.
    #12