vf750f fuel pump maybe dying?

Discussion in '1st & 2nd Generation 1983-1989' started by beeton, Oct 17, 2022.

  1. beeton

    beeton New Member

    Country:
    Canada
    Joined:
    Sep 28, 2010
    Messages:
    73
    Likes Received:
    2
    Trophy Points:
    8
    I can't seem to find the search bar for this question and I have searched though search engines.

    I have an 84 vf750f. The bike is slowly being cleaned up. The bike was running fine as I had balanced the carbs, tried to set the pilots (maybe a bit off).
    The other day, hard to start. the bike would catch and then die after a few moments.
    I checked the pump connections, all good. Checked the relay as per instructions found in searches and seemed good.
    I check the pump by applying 12v directly to the leads and it "pumps" once-three times then stops.
    I remove the pump and apply 12v, pumps without any issue (no lines attached so I did not run for more than a few seconds).
    When I try the 12v directly, and the pump does NOT have any line attached to the exit port, seems to kick in fine but if I attach a line or even put my finger over the exit port, stops pumping.
    There must be an internal back pressure switch that is failing.
    Does this make sense and if so, would you know the pressure of this pump (likely 7-9 pounds) as I have to buy a replacement. I have an in-line pump that will work but not the best fit under that area so a "stock" fit would be better as these are nla from Honda (and I don't want to pay $200 for it either).

    Thanks.
     
  2. RogueRC24

    RogueRC24 New Member

    Country:
    United States
    Joined:
    May 25, 2021
    Messages:
    707
    Likes Received:
    186
    Trophy Points:
    43
    Spit ballin.. What if you try an exit line that goes into a empty bottle? Will fuel actually pump out of the pump? If so maybe there is a clog in the carb that has enough back pressure to set of the pump stop? Maybe that will at least take the carb or the fuel pump out of the equation.
     
  3. squirrelman

    squirrelman Member

    Country:
    United States
    Joined:
    Jul 27, 2006
    Messages:
    9,444
    Likes Received:
    591
    Trophy Points:
    128
    Location:
    Buffalo, NY
    Map
    sensing pressure, the pump shuts itself off when the carbs are full or outlet hose is blocked.
     
  4. beeton

    beeton New Member

    Country:
    Canada
    Joined:
    Sep 28, 2010
    Messages:
    73
    Likes Received:
    2
    Trophy Points:
    8
    I will try that again and report back.
     
  5. beeton

    beeton New Member

    Country:
    Canada
    Joined:
    Sep 28, 2010
    Messages:
    73
    Likes Received:
    2
    Trophy Points:
    8
    O.k. So I will check it again without the fuel filter to see if the pump will pump into a bottle (no back pressure). The pump shut off as soon as I placed a finger on the outlet, seems the back pressure sensor is very sensitive. It could be that the pressure part is wearing out.
     
  6. squirrelman

    squirrelman Member

    Country:
    United States
    Joined:
    Jul 27, 2006
    Messages:
    9,444
    Likes Received:
    591
    Trophy Points:
    128
    Location:
    Buffalo, NY
    Map
    not at all likely. pump is rated at 3 psi.
     
  7. Terry Smith

    Terry Smith Member

    Country:
    New Zealand
    Joined:
    Nov 18, 2013
    Messages:
    2,553
    Likes Received:
    513
    Trophy Points:
    128
    Location:
    Auckland, New Zealand
    Map
    Sounds to me like your pump is fine; it keeps pumping until the fuel line is full and the carb float valves are shutting. There's no "internal back pressure switch" the pump simply stalls when it can't push any more into the line, and three cycles sounds about right. I know on my 86 that the fuel pump would click every few seconds when the bike was idling as fuel was being used.

    Rogue's suggestion is sound, if you are concerned then stick a hose on the outlet and let it pump to a jar.

    You can check whether there is plenty of fuel at the carbs by opening the bowl drains. Once empty, shut them off and re-test the pump, it should run quickly for quite a few seconds then slow and finally stop as the bowls get refilled.
     
Related Topics

Share This Page