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Slight Issue With My Zxr750

Discussion in 'Mechanical' started by S92Jockey, Sep 5, 2016.

  1. S92Jockey

    S92Jockey Learner

    Messages:
    6
    Hi all...
    Before I can hit the road with you all, and after having rebuilt my bike, I appear to have a small issue..

    It only appears to start and run when the tank is over half full....
    So, does this seem to be a fuel pump problem..
    It has been rebuilt with all new fuel lines, filter and the carb has been cleaned and set up, (runs beautifully with a full tank)....!!!
    Also, should the pump run for a short time to prime the lines when the ignition and run switch is on, as it does not or, does the pump only run when the engine is running....?

    My guess, it perhaps is the pump, as the beast will only start with a good head of fuel pressure in the tank.....
     
  2. BlackHornet

    BlackHornet Look before you turn Staff Member Moderator +

    Messages:
    7,536
    Does the pump click on start up?
    Or could there be a pinched breather pipe somewhere?
     
  3. S92Jockey

    S92Jockey Learner

    Messages:
    6
    Hi Black..
    Thanks for you're reply..
    No sound, at all, from the pump, and all breather pipes appear to be fine..
    I'm going tone place the pump, and will go from there.. :)
     
  4. BlackHornet

    BlackHornet Look before you turn Staff Member Moderator +

    Messages:
    7,536
    Yeah if there isn't a sound then it's not working :) you could try connecting the battery straight to it before removing to make sure it's not just a loose connection before you replace it.
     
    S92Jockey and Mikey like this.
  5. S92Jockey

    S92Jockey Learner

    Messages:
    6
    Ok... I bought a new pump, fitted it and the pump is working...
    When I hot wired the old pump to the battery, first off it didn't work, second attempt it did.... But,
    The voltage to the pump is only around 5v while cranking and at idle... Gradually increasing with RPM. (Pump only works with engine running)....
    Is this normal...???
    Battery voltage at rest is a little over 12v... Over 14v volts across the battery while running, so alternator appears to fine....
    Answers on a postcard pls
     
  6. BlackHornet

    BlackHornet Look before you turn Staff Member Moderator +

    Messages:
    7,536
    The pumps only work if the fuel is running, either being used up by the engine running or if you pump the fuel into a container, if the fuel isn't being used or going somewhere the pump thinks it has done it's job. no idea about voltage I still just stick my tongue on the battery to see if it's good :p
     
  7. hoppielimp

    hoppielimp Fair Weather Rider +

    Messages:
    2,168
    uhmmm i don't think its normal. you should be getting close to 12v at the pump. I am not an expert at this, but the two things I would check are 1) Your relay is not oxidised up...as this will cause a bad connection and hence a low voltage... 2) Check the voltage drop on the power side and at the ground side of the pump...I believe the drop should not be more than 0.5V

    Since you have a new pump, it is unlikely that it is at fault....so it looks like wiring...the question is where...

    edit/Whilst on the relay...you could also check that the relay itself is putting through 12V
     
    S92Jockey and BlackHornet like this.
  8. S92Jockey

    S92Jockey Learner

    Messages:
    6
    Ok, thanks Hoppie....
    Will check and let you know :)
     

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