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Thoughts on fuel pressure and lean condition

Discussion in 'BNS12 Chat & Tech' started by NPS, May 18, 2019.

  1. NPS

    NPS Cruisin' Guzzisti GT Contributor

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    Today the fuel condition suddenly changed on my Breva 11. I have an air fuel ratio meter on the bike linked to a wide band so I was able to see a different AFR and a loss of power.

    The problem was the usual 13.5 to 15 AFR suddenly changed to 15.5 to 16.5 range at any engine speed and throttle opening above 1800 rpm.

    When I removed the fuel tank, I noticed that fuel continues to run from the red pipe without stopping. I have only had a few dribbles before so this has changed. I'm wondering if a valve has failed and this is reducing the fuel pressure. The pump sounds the same.

    Any thoughts anyone?
     
  2. Brian UK

    Brian UK GT Reference

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    Fuel should not run from that connector when disconnected, so you do have a problem somewhere. Pull the pump unit out and check.
    And then change the fuel filter for an all metal one if it still has the half plastic version.
     
  3. john zibell

    john zibell Moderator Staff Member GT Famiglia

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    After what Brian has suggested, find a location to connect a pressure gauge. The fuel system pressure should be about 3 bar or 45 psi. If pressure is less then it is time to replace the fuel pump unit.
     
    NPS, V700Steve and Didier like this.
  4. V700Steve

    V700Steve High Miler GT Contributor

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    Bike that age I would think a crack in manifold rubbers or in stepper lines to TB's would be first to look for lean condition.
    I get fuel from line but it usually stops at sometime. I would think the built in pressure regulator on the base plate would shut it off w/o pressure coming from pump. I thought some of those are replaceable.
     
  5. NPS

    NPS Cruisin' Guzzisti GT Contributor

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    Got the bike running sweet by temporarily adjusting the ECU Fuel-temperature table by +10%. Makes the bike run better than I have ever known. But I realise a failing fuel pump or valve is something I must checkout and will when the fuel level gets lower in the tank. Thank you Brian, Steve and John for your comments. The rubbers should be fine as I replaced the manifolds last year and the stepper motor tubes are ok on visual inspection.
     
    V700Steve likes this.

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