airhead balancing act

Discussion in 'Airheads' started by noz, Jun 27, 2010.

  1. noz

    noz Adventurer

    Joined:
    Mar 28, 2010
    Oddometer:
    52
    ok what am i doing wrong with balancing the carbs.

    i'm going for a ride to warm her up, gettting the idle in balance .1000
    then once that fine i balancing the throttle at 1500-2000.

    She seems fine all nicely in balance.
    then nexdt day i go for a ride even when i broght it back after about 20 mins still lumpy idle at 700 odd rpm like it wasnt warm. am i balancing it wrong?

    using home made manometer to balance it.

    someone help making it hard to ride.
    #1
  2. tres

    tres Quixotic Adventurer

    Joined:
    Nov 13, 2009
    Oddometer:
    21
    Location:
    Seattle
    I think the problem is that the idle jets are still not balanced. The idle jet is balanced via the screw underneath the exit port of the carb. When balancing at 1.5k - 2k, you're balancing the mains. So you could have an excellent ride as soon as you start opening the throttle, but chortle and die as soon as you take your hand off the throttle.
    #2
  3. noz

    noz Adventurer

    Joined:
    Mar 28, 2010
    Oddometer:
    52
    i start out by balancing the idle using the srew adustment underneath with no problem .

    then move onto the cable to see the load balance and get that so there no difference.
    if i took it for another right there and then it would be fine.
    #3
  4. borg

    borg Been here awhile

    Joined:
    Aug 22, 2005
    Oddometer:
    123
    The screw "under" the carbs is the idle mixture screw, depending on your model these will be some where between 1 and 2 full turns out from seated to start with. Once the bike is warm you fine tune these by ear until you get the fastest/smoothest idle going on that cylinder. Once both sides are smooth then adjust the idle speed using the screw for that, it's the one you access from the top, you'll see it working on a small lever arm. Once your idle is set then you can work on part/full throttle adjustments which is really a matter of adjusting the amount of freeplay in the cable sheath-to-carb distance until both carbs are coming off idle at the same time.

    I highly recommend getting the Bing manual. Also make sure everything else is good, choke is closing all the way, no air leaks etc

    Steve
    #4
  5. tres

    tres Quixotic Adventurer

    Joined:
    Nov 13, 2009
    Oddometer:
    21
    Location:
    Seattle
    Sometimes it's helpful to take nothing for granted. If you haven't taken them apart & verified that the needle positions are correct & that everything is clean enough to function correctly, it might help.

    I've heard stories of people who opened up their Bings to find that a PO created mess that would make it impossible to ever balance.
    #5
  6. tres

    tres Quixotic Adventurer

    Joined:
    Nov 13, 2009
    Oddometer:
    21
    Location:
    Seattle
    I recently had a very similar issue.

    I had installed some Bings for an R65 that I had put R100 jets in. I changed the slide out, & changed needle position on the main & changed the idle jet to the same size used on a 100/7. I cleaned everything, installed new o-rings, diaphragms & floats. Pretty much brand new.

    The idle would work well during startup, but that's because the Boyer electronic ignition keeps the engine up above 1k for the first few minutes. Once things got warmed up, the Boyer wanted to drop down to 600 - 800 rpm.

    And once that happened, there was no way to keep that engine running at idle until it was completely warmed up (and even then, I still had issues sometimes). I really hated trying to finesse that throttle every time I needed to slow or stop for the first 10 miles.

    I had recently changed out the flywheel/clutch/transmission to a post 1981 version -- much lighter & so I thought that the Boyer just relied on the heavier flywheel. I changed to another ignition only to find the same problem still existed.

    So long story short, I put some carbs intended for an r100 onto the bike & never had that problem again. Now it's like brand new.

    Probably not relevant for you or 99% of everyone else out there, but if you do have carbs that weren't intended for your bike, it may be the problem. There are some press-fit parts that just can't be changed out.
    #6
  7. Renner

    Renner combustophile

    Joined:
    Jul 11, 2007
    Oddometer:
    2,762
    Location:
    sunny SoCal
    some confusion regarding idle mixture vs. idle speed adjustment screws because the year model is not specified.

    /5s have idle mix & adjust at the bottom and close together. Later model carbs the idle speed adjustment moved to the top.

    What bike is this and are the carbs original equipment for that year?

    When making adjustments (I like the manometer too) are you running a sizeable fan in front of the cylinders. Also some slack in the cables at idle?

    just checking.

    Points ignition?

    I find if the idle is set a little high the advance mechanism can come into play, advance increases and idle comes up further increasing advance...

    Maybe try 800 rpm idle.
    #7
  8. jtwind

    jtwind Wisconsin Airhead

    Joined:
    Nov 19, 2004
    Oddometer:
    3,474
    Location:
    Madison WI
    #8
  9. noz

    noz Adventurer

    Joined:
    Mar 28, 2010
    Oddometer:
    52
    thanks everyone for helping.

    Rite the bike is a 76 r75/7 with origional 64/32/13 and 14 carbs
    i have rebuilt the carbs including all orings new floats and needles. checked for leaks and the choke systems has been checked for orientation and operation. Also butteryfly marked before dissasemble. reinstalled as good and i can get it for no light around it.

    the carbs have the idle adjustment screw underneath aswell as mixture
    mixture set at 3/4 out.

    i have read the balancing guide and it doesnt say to adjust the mixture any more than setting to spec.

    i have retro fitted the later carb springs to stop the slides hanging up.

    i could well be getting the slack wrong.

    i have been litteraly getting the balance of idle of 1000rpm with the cables not afftecting it them setting the cables. in balance so they dont affect the 1000rpm and balance clean on the manometer with slight slack on the throttle.

    have just been out for another ride mid way through there it was fine brought it back and lumpy idle again.
    #9
  10. noz

    noz Adventurer

    Joined:
    Mar 28, 2010
    Oddometer:
    52
    hang on maybe it me with the setting of the mixture, and finding the sweet spot for it and not setting it for the sweet spot before setting the idle after that.

    would this cause these irregularities?
    #10
  11. Xcuvator

    Xcuvator Justa Venturer

    Joined:
    Jul 23, 2007
    Oddometer:
    1,374
    Location:
    Skolls Or
    By any chance, when you have the lumpy idle, do you have the bike in gear with the clutch pulled or is the bike in nuetral? I had a bike that would slow down at idle when warm with the clutch pulled.
    #11
  12. borg

    borg Been here awhile

    Joined:
    Aug 22, 2005
    Oddometer:
    123
    You do have to chase these two around the block a few times before finding the sweet spot.

    Steve
    #12
  13. Prairie Beemer

    Prairie Beemer Adventurer

    Joined:
    Oct 5, 2008
    Oddometer:
    52
    Location:
    Saskatoon, Saskatchewan, Canada
    Make sure there's a little slack in your throttle and choke cables. Check for any intake leak. Carb floats moving freely? Since you're in there, why not clean the idle jets?
    #13
  14. rufusswan

    rufusswan Been here awhile

    Joined:
    Nov 16, 2007
    Oddometer:
    962
    Location:
    Branson MO
    That is the starting point. You must get the bike to idle and run so you can ride it for 15 minutes. Then you can start to chase mix/idle speed around as borg said until you are happy.

    I assume you mean throttle return springs which are to make sure the butterfly closes on the idle stop. Your slides should not 'hang up'. When on the bench they should smoothly go from end to end when you turn the carbs over, or suck/blow into the vacuum hole in the carb throat.
    #14
  15. P B G

    P B G Long timer

    Joined:
    Mar 7, 2008
    Oddometer:
    10,001
    Location:
    Greater Chicago
    What he means are the springs above the slides, those big loosely coiled things. Some carbs didn't have them oem, others do. They shouldn't hang up, but some might w/o springs sometimes.

    Every spring before I do this job I make sure of a few things.

    New air filter,
    Valve adjustment,
    Ignition system check up.

    THEN I move onto the carb balancing. Its tempting to put off these things and tune the carbs so you can ride, then later on you decide you'll check the valves and change the air filter and such. Do it first. Its better.
    #15
  16. Bigger Al

    Bigger Al Still a stupid tire guy

    Joined:
    Oct 12, 2004
    Oddometer:
    8,263
    Location:
    Auburn, CA
    Did you adjust the valves before trying to synch the carbs?

    *edit*

    Of course, it would prolly make some difference if I read every post before replying myself. :baldy :lol3
    #16
  17. Plaka

    Plaka Brevis illi vita est

    Joined:
    Jun 19, 2010
    Oddometer:
    4,623
    If you are happy when you are done tuning but unhappy after a ride, then something changed. But what?

    Bike at the same temp? Not properly warmed up will hurt as will overheated after a ride?

    Wrong or worn plugs? If the plugs are partially fouling during tuning and then cleaning themselves during a ride the tune will change.

    Valves dead on (including rocker end shaft play)? set them dead cold and check them again dead cold if the tune changed. You did torque the heads before setting the valves, right?

    Air leak check? (you said you did, did you use ether?)

    Tuning on the centerstand, right?

    Throttle cables completely slack when setting up idle? (not 1/16", 1/8" +++). Throttle assembly free, lubed? If you have a splitter cable is it in good shape?

    Personally I don't use a manamoter for balance. I had an old BMW wrench teach me to power balance and it worked well. I tried a Walus setup once and it just wouldn't cut it. The power balancing is faster and incredibly accurate---and you set it up for your most frequent cruising speed so you always are running in the sweet spot. On an airhead, especally as the miles pile on, the manifold vacuum corelates poorly with the power output. The left side usually has more compression. So you balance the thing for power, not vacuum. Makes for very smooth running. In addition it provides a couple of in process diagnostic moves that you can quickly repeat later if things aren't right.

    Do your valves and timing. Warm it up with a ride (I don't do the ride but I have do measure temps and most people don't have that gear).

    Slacken the throttle cables completely and fully back off the butterfly stop screw so both throttles are completely closed. lift up on the throttle lever and release to ensue the springs fully close those throttles. A PO may have fitted softer springs. Beware.

    Set the butterfly stop screws to initial position per manual. You must know exactly when the screw touches down so you can start counting turns. Try a bit of cigarette paper as a feeler gauge if you have to. It's not dead critical though.

    Set idle mixture screw to initial setting per manual. Don't tighten it in real hard---just till it's closed then back it out. It's got a good o-ring on it, right?

    Start the bike and it should idle. If not you gotta problem. Diddle the idle mixture screw on one side until it runs best. Repeat on other side. Go back to first side and see if a little diddling makes better. Ditto the other side. Now the idle mixtures are set. If one screw position is vastly different than the other you gotta problem.

    Shut it off and fit the shorting wires.

    Start it, let idle a half minute then short one side with the insulated screwdriver. The running side should hit 2-3 times then die. For higher idle it should hit 3-4 times then die. Adjust the butterfly stop screw to get this.

    Now short the other side and repeat. 2-3 hits then dies. Adjust the butterfly stop screw on the running side again. If the settings on the two screws are vastly different you gotta problem.

    Now the idle mixture and speed are done. If you want a higher idle turn in both butterfly stop screws exactly the same amount---and it's a very tiny amount. Wait 30 secs. between adjustments for the motor to catch up. Never touch the throttle or throttle cables.

    If you are new at it (hence low) watch your engine temp. Let it cool some or fire up the fans.

    Remove the slack from the throttle cables. Take it to just barely peerceptable slack. Work the throttle at the handlebars a couple times to WFO and back and makes sure things are right (slightest slack) at the carbs.

    Start it up again. Take it just off idle and then short one side, with the throttle ind it up to cruising rpm and lock the throttle so it does not move (throttle lock screw, this is where you use it).

    Rapidly switch the shorting to the other side. Have both screwdrivers touched down on the shorting wires and just slide one forward to contact the head and the other back to break contact. helps to watch someone do it once. The rpm should not change. Go back and forth a time or two to identify the weak side. Shut it off and tighten the throttle cable on the weak side. Experience will reveal how much to try at a time.

    Fire it up and repeat. Continue finding and correcting the weak side until there is no (as in none) change in rpm when you change from one side to the other. Tighten the cable lock nuts and you are done.

    If one cable needed a whole lot of tightening to get it balanced, something may be funny. Keep it in mind.

    If you ever un-short BOTH sides when you have it wound up to speed on one side only then the engine will run away---fast. So don't do that. Better to short both sides by accident and just kill it.

    Now if you are unhappy the following day you put your shorting wires on and short one side at idle. Then try the other side. If the balance is way off then either the butterfly stop screws moved, you had some procedure error in the beginning, the butterfly aren't closing against their stops or the idle mixture got hosed (aside from a valve adjustment issue, etc.)

    Check the mixture screws at idle. Diddle each one a little and see if a change is required to get one or the other side to idle best again. if they need readjustment there is something funny in your idle circuit. Try running some Seafoam to clean things and check the idle mixture screw o-ring, the tip of the idle mixture screw for ridges or being mashed or maybe even bent. Make sure the idle jet and whatnot is clean and seated. Make sure the carb bowls are clean and you aren't sucking crap (like water).

    Beware the choke cover gasket. A common failure. Leaking diaphragms can also give you grief as can a worn needle/needle jet. See the Bing manual for Dx.

    If you do use a manometer you introduce a change as soon as you are done---the manometer is no longer connected and you put the screws back to plug the holes in the carbs. Check the washers under those screws.
    #17