Adjusting carb on Sport bike motorcycle

Discussion in 'Off Topic' started by davidsis, Jul 15, 2009.

  1. davidsis

    davidsis Guest

    A friend of mine bought this sport bike and he is complaining that it is back fireing. He thinks it is the carb. He replaced the carb a couple of mounths ago, and He think it needs synchronized or something. I think it could also be bad plugs like maybe not the right plugs or something. It is an in line 4 and has 4 carbs. Anyone have any experience with sport bikes and adjusting the carb on them, or can anyone point me in the right direction? Or what do you think it is? Is back fireing a typical carb thing?
     

  2. arceeguy

    arceeguy Active Member

    If the bike has been sitting for a while, he'll need to fully disassemble all the carburetors and rebuild them. After that, the carbs will need to be synchronized and balanced with a set of vacuum gauges.

    Just trying to adjust them is probably going to be a time waster, unless he knows for sure that the carbs aren't all gummed up from long term storage.

    Here is a short tutorial:

    http://www.motorcyclistonline.com/howto/motorcycle_carb_sync/index.html

    Note: if you use the mercury type gauges, do not abruptly close the throttles shut as this may draw mercury into your engine. As you know, mercury is toxic, so we don't want any being passed through the engine and out the exhaust! I doubt they sell that type of gauge anymore for obvious reasons, but there are probably millions still out there.....
     
    Last edited: Jul 15, 2009
  3. davidsis

    davidsis Guest

    Synchronizing

    The symptoms are different. It doesn't surge at idel speed or idle eratically, it back fires, I am not sure at what speed though. I will have to ask some more questions.
     
  4. arceeguy

    arceeguy Active Member

    The idle circuits in the carbs can be clean, allowing the engine to idle acceptably - but the midrange and main circuits can be partially blocked. This leans out the mixture causing flat spots in acceleration and backfiring through the intake.
     
  5. Mountainman

    Mountainman Active Member

    could be a timing issue ??
    a rough way to set timing is
    to advance until pinging
    take it back (retard) just a little
    should be pretty darn smooth
    not rocket science
    but grandpa taught me
    comes out pretty darn close
    MM
     
    Last edited: Jul 15, 2009
  6. arceeguy

    arceeguy Active Member

    We actually need to know a lot more about this bike before anyone could even guess as to what's wrong. (and even then, it would just be a stab in the dark) Make, year, model. When it "backfires". If it "backfires" out the carburetors (a true backfire) or out the exhaust. Etc. and so on.
     
  7. davidsis

    davidsis Guest

    Sport bike

    It is an 89 Katana gsx, I will check on where it back fires from, he mentioned it also cuts out loses power some time. Oh ya also he has a vance and hines exuast where they all go into one instead of two exaust pipes like it came stock.
     
    Last edited by a moderator: Jul 18, 2009
  8. Mountainman

    Mountainman Active Member

    some of the time

    some of the time ???
    sounds possibly like elect
    fuel (((usually)))((( will be))) all of the time

    MM
     
  9. biken stins

    biken stins Member

    Why doesn't he have a manual for it. There is a proper order of trouble shooting problems such as he is having.
    Get a manual of Amazon .
    Put some pedals on it .
    These kind of problems makes me glad to have a single cylinder.
    got fuel-check. got spark-check-half choke & pedal faster.
    Seems bikes left out for awhile do have problems. No one remembers why it was parked.
    Good luck.
     
  10. davidsis

    davidsis Guest

    ((usually all of the time))

    what does ((usually all of the time)) Mean. What do you mean by that?
     
  11. arceeguy

    arceeguy Active Member

    When a motorcycle has been parked for a while, and won't run correctly when taken out of "dry dock" - it is usually something with the fuel system. (unless it had other issues, causing it to be parked, as biken stins pointed out) A good starting point is to remove and rebuild all of the carburetors. The carb kits come with instructions for setting float level and adjustment screws to baseline settings, but I would also consider a service manual necessary. If the bike is sagging and surging, the fuel system is where to start. Electrical and ignition timing problems usually manifest themselves differently.
     
  12. Mountainman

    Mountainman Active Member

    changes day to day

    usually all of the time ???

    today I think that means 90% of the time

    maybe tomorrow it will be 85% or 95% ??

    fuel problems usually don't come and go
    unless
    fuel pump problem ??
    filter getting plugged a little then letting up when not in use ??
    bad sticky gas ??

    MM
     
    Last edited: Jul 19, 2009
  13. davidsis

    davidsis Guest

    Re jet

    He said that he thinks the carbs need to be re-jetted because of the exuast. Anyone have any experience with re jetting? Does this sound right. need to be re-jetted.
     
  14. arceeguy

    arceeguy Active Member

    If there were changes made to the intake or exhaust, the jetting will need to be changed to match the new flow characteristics. Rejetting a set of four carbs is probably best left to a professional, as buying sets of four main jets, jet needles, or pilot jets can get expensive. A seasoned tuner can drive the bike and find out which circuits needs adjustment. For example, mid throttle bogging needs a different jet needle and/or needle jet. WFO bogging needs a larger main jet. Off throttle bogging/stumbling may need a larger pilot jet along with adjusting or replacing the jet needle. A very delicate art!

    Was he the one that made the changes to the exhaust that caused the backfiring? Or did he acquire the bike that way.
     
  15. davidsis

    davidsis Guest

    Acquire the bike that way.
     
  16. Mountainman

    Mountainman Active Member

    would the THING really need jetting ???

    would the THING really need jetting ???

    you know those carb THINGS for adjusting duel carbs
    been a while but
    plastic THING with some floting balls I think
    a guy that knows how to use one of those can work wonders with carbs

    bought an old BSA 250cc one lunger once apon a time
    THING ran like crapperstuff
    somebody has changed the needle gas jet
    once I got the close to right one back in

    hold on to that THING -- kind of anyway

    MM
     
  17. davidsis

    davidsis Guest

    Call me crazy but I might try to adjust his carb. Well I am going to try to fix his bike. Anyone know of a good motorcycle repair web site. one that is a suzuki web site that is the equivilant to this one only for Suzuki?
     
    Last edited by a moderator: Aug 5, 2009
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