Observations on my first real airhead ride

Discussion in 'Airheads' started by drooartz, Aug 22, 2010.

  1. Plaka

    Plaka Brevis illi vita est

    Joined:
    Jun 19, 2010
    Oddometer:
    4,625
    With both petcocks open, you are getting plenty gas to the carbs, no matter what.

    Pop the float bowls, insomuch as it takes 2 seconds and have a look. Fine sediment or water globs indicate a tank flush and need to fit filters. I always run filters...and watch them fill up with crap too. The stuff in a lot of gas pumps is crummy and you never know what the last guy got in the end of the hose. Never buy gas if there is a tanker filling the gas station tanks.

    If the diaphragms are bad it is bad all the time. un-mistakeable. If the jetting is off it wwill be gutless and run hot---but smooth. Air leaks at the carb or the carb-to-head rubbers will lean it out too. But simply examining the plugs will reveal this. The next time it is stumbling kill it and cheeck the plugs.

    I would most suspect an ignition issue---weak sparks from old coils or bad wires or old /dirty plugs. This shows up most under load and it is a stumbly sort of effect, not smooth but gutless.

    I'd give it a basic tuneup, plugs points, check the plug wires and also the coils before I messed with the carbs. And then don't mess with the carbs unless you have balancing issues (idle air screw does nothing for example) or plug chops reveal a mixture problem.



    Beware the front brake if it is damp inside and your speed is low.
    #21
  2. drooartz

    drooartz Been here awhile

    Joined:
    May 8, 2007
    Oddometer:
    125
    I drained and pulled the tank last night. Blew out the petcocks and they seem to be working fine. I'll replace the in-tank screens. Inside of the tank doesn't look too bad at all. There was a bit of gunk on the internal screens, but not too much.

    Before I pulled the tank, I did a quick test run with the external inline filters removed and still got the issue (not surprising). I've got a carb rebuild kit coming from Hucky. I'll pull the float bowls after work tonight and see what's in there. Carbs look pretty grungy from the outside, so I don't mind digging in an cleaning them up.

    Plugs and plug wires are new, points were set by a known good BMW mechanic (ie not me :D ). Coils were not replaced.
    #22
  3. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Check the point gap anyway. Sometime's they'll wear in after a few hundred miles and close up. 0.016" or 0.4mm. Make sure a dab of distributor cam grease is rubbed into the felt pad on the breaker plate.

    Remember, you have a new-to-you bike and although it's been well-maintained, assume nothing. You're zeroing out the maintenance history.
    #23
  4. kta

    kta Been here awhile

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    I had the same issue when I picked up my /5. Turned out one of the floats was set just slightly too low. The bike would starve a bit when on the throttle. Raised the float a smidge, problem solved.
    #24
  5. drooartz

    drooartz Been here awhile

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    May 8, 2007
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    125
    To wrap this thread up, I put some time in over the last week and rebuilt the carbs (new gaskets/o-rings, throttle shafts, jets, cleaned everything carefully) and cleaned out the petcocks. New in-tank screens and new inline filters (from Bing).

    Got the bike reassembled yesterday and took it for a quick spin. Acceleration is much improved, and the stumble is gone. Woohoo :clap
    #25
  6. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Yep. Even though carbs can "look good", unless you know it's been done recently and correctly, it's a good idea to re-do the carbs. Eliminates one area of questions.
    #26
  7. lkchris

    lkchris Albuquerque

    Joined:
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    1,097
    Nah, Bings self-adjust for altitude--thinner air means less diaphragm deflection.
    #27
  8. Renner

    Renner combustophile

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    Most excellent, dude.
    Ride on.
    :super
    #28
  9. fishkens

    fishkens Long timer

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    Kent, I'm surprised to hear you say that. My Bing manual clearly addresses the possible need to reduce main jet size for higher elevations. Granted, you don't need to change jets for a two week tour through Colorado but when I moved from sea level to Santa Fe (and another time to Ft. Collins) I went to a smaller main jet and dropped my needles.

    Depending on where the bike was tuned for previously, if he's going to regularly ride at > 5K - 10K feet adjustments may be in order.
    #29
  10. drooartz

    drooartz Been here awhile

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    Once I get used to the bike I figure I'll need to dig in a bit and see if it is running too rich. Easy enough to tweak once I know what needs to be done.
    #30
  11. bmwhacker

    bmwhacker Still on 3 wheels

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    Those darn little gaskets on the choke enrichment assembly always deform and curl up at the little loop. Hope you replaced them too. (borrowed photo from Hans)

    [​IMG]

    Great looking bike....I've run /5's for the past 20 years. They require a lot of fondling but the great experience of riding them far outwieghs the effort.
    #31