carb problems i think

Discussion in 'Motorbike Technical Discussion' started by bigblock_hotrodtruck, Mar 14, 2007.

  1. I have a 1981 honda cb 650 costum,it idles fine but when you go down
    the road it cuts out real bad around 3500 rpms. It ran fine last
    summer but this morning it went south. does any-one out there have a
    recommendation on a home fix for this problem?
    bigblock_hotrodtruck, Mar 14, 2007
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  2. <Holds head in hands and whimpers>
    The Older Gentleman, Mar 14, 2007
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  3. Maybe you should go on the wagon for a while?
    Potage St. Germaine, Mar 14, 2007
  4. Pull the fuel hose off the carburetor and drain some gasoline into a
    clean container. Is there water or rust in the gasoline?

    If not, your idle jets and idle passages and ports are probably just
    getting plugged with gum and varnish.

    Riders who store their motorcycles over the winter without
    putting Stabil in the gasoline notice that the engine will start and
    idle, but won't run above about 1/4 throttle without cutting out due
    to fuel starvation...

    Run down to Wal*Mart or any good auto parts store and purchase a can
    of Berryman B-12 Choke and Carburetor Cleaner for about $3.25.

    The 15-oz. can of liquid B-12 works best, but if you can't get that,
    buy some B-12 or STP or GumOut carburetor cleaner in the aerosol can.

    They all contain xylene, methyl alcohol, toluene, acetone, etc, and
    those solvents will clean gum and varnish out of the carb as you ride.

    Don't buy Techron, or any fuel system cleaner that contains "petroleum
    distillates". Those cleaners are for fuel injectors.

    Carefully measure about 4 or 5 ounces of the carb cleaner into a
    container and pour it into a full tank of gasoline and go for a slow
    ride, using as little throttle as possible to make the carburetors
    suck gasoline through the idle jets.

    After several miles, you should notice that the engine is idling
    faster, so you can turn the master idle knob down.
    It's probably located between the two carbs on the right hand side of
    the motorcycle.

    If cleaning the carbs doesn't "get 'er done", it's possible that your
    spark plugs have reached the end of their service life. Spark plugs
    cost $2.50 to $3.00 each, so you're looking at $10 to $12 for spark

    But modern motorcycles with electronic ignitions don't
    have a lot of problems with spark plugs, rough running at low RPM is
    caused by dirty carburetors and cutting out at
    very high RPM is caused by old spark plugs.
    Potage St. Germaine, Mar 14, 2007
  5. bigblock_hotrodtruck

    John Johnson Guest

    There, there, TOG, 3 fingers of single malt will set everything aright.

    As for the OP, did you happen to drain the gas out of your carbs before
    letting the bike sit for 6 months? If not, they're almost certainly
    plugged, and you're going to have to clean them out. You might try the
    Yamaha or seafoam cleaner that you fill the carb bowl with, let sit for
    30 minutes, and flush out, but more likely it's going to require pulling
    the carbs, disassembling them, and thoroughly cleaning them. This
    procedure has been posted on this list _many_ times, so search the group
    archives (e.g. via a google-groups advanced search) for details.


    'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.
    John Johnson, Mar 14, 2007
  6. <Hopeful>

    Are you offering?
    chateau.murray, Mar 14, 2007
  7. bigblock_hotrodtruck

    John Johnson Guest

    Man, you live closer to the stuff than I do! I'm more of a rum drinker
    in any case. I will toast you next time I have a sip, though. :)


    'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.
    John Johnson, Mar 14, 2007
  8. I was sipping a lovely cask strength (56% ABV) Bowmore the other
    day.... Nectar, it was.
    chateau.murray, Mar 15, 2007
  9. bigblock_hotrodtruck

    John Johnson Guest

    Funny. I've had two friends talk to me recently about Bowmore (one was
    referring to their double barrel, IIRC. the other has a bottle of their
    "Legend"). I'll keep an eye out for the cask-strength next time I'm


    'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.
    John Johnson, Mar 15, 2007
  10. Afraid not. The battery will put out slightly over 12v and it will run
    happily on that. The charging system generally puts out over 13v, but it
    doesn't need this much to run properly.
    The Older Gentleman, Mar 17, 2007
  11. bigblock_hotrodtruck

    Paul Barrett Guest

    OTOH, I chased a problem like this for quite a while with a CB750, and it
    turned out to not be the carbs at all, but the damn spark plug wires.
    Ran fine at low RPMs but cut out at 4-5K.
    Still, the carbs are probably more likely, esp. if he hasn't tried the
    Berryman's yet.

    Paul Barrett, Mar 20, 2007
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