Loosing fuel pressure when hot

Discussion in 'Engine Topic' started by snowcone, Apr 11, 2015.

  1. snowcone

    snowcone Veteran Member

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    Hi again

    I finally got my new motor running pretty good but now I'm having problems with my fuel pressure drooping to anywhere in between 2-5psi.

    When i start it up cold my fuel pressure fluctuates between 6 and 6.5 psi and as it starts to run smoother as it warms up it levels out right at 6psi. I noticed the pump is much louder when cold and then quiets down after a few minutes of run time.

    After about 20 minutes of running (if that even) it will drop down between 2-5psi. The gauge is one of the cheap summit gauges but i have ruled that out of the equation because it develops a terrible bog/shudder when the pressure drops. I also tired wrapping the gauge in a ice bag to see if the heat was effecting the gauge but the reading did not change.

    My tank is vented and i am using a Holley return style regulator with a carter low pressure pump 8psi. I am running a filter before the pump and right before the carb.

    Any ideas? I'm thinking I'm going to have to drop the tank to check and make sure the pickup isn't getting clogged.
     
  2. snowcone

    snowcone Veteran Member

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  3. ssenay72

    ssenay72 Veteran Member

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    Electric pump? If so where do you have it mounted?
     
  4. ssenay72

    ssenay72 Veteran Member

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    sorry pics showed up right after I hit enter, anyway electric pumps like to push rather than suction fuel. I had a holley pump mounted way too far from the gas tank and it would whine like crazy. (even with a sump style tank) moved it and problem solved. So you could have fuel starvation. Doesn't make sense its fine until it gets hot but that could be the pump overworking to get fuel.
     
  5. snowcone

    snowcone Veteran Member

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    Thanks, when I mounted the pump I had that in mind, but that was the best place I could find to mount it, i figured the inlets were far enough on the bottom of the tank but maybe not. Where did you end up moving your pump too?
     
  6. Damon

    Damon Veteran Member

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    First off, you test the regulator and pump by clamping off the return line and seeing if the pressure goes back up. Given the pump is only 8 PSI this is unlikely to cause any problems or immediately flood out the carb.

    That's not a liquid-filled gague, is it? I hate liquid-filled gagues. They ALWAYS go flaky on you sooner or later (usually sooner).

    Your pump is low enough that it's not going to be a problem sitting still or driving around normally. Might be a problem when you go WOT in the lower gears, but that's not today's problem.

    Clamp off the return line, report back.
     
    Last edited: Apr 11, 2015
  7. snowcone

    snowcone Veteran Member

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    Thanks Damon, I will try clamping the return and see what happens, I never thought of that. Im leaning towards a clogged line somewhere because even idling in park now it seems to hesitate for just a second when you try and Rev it, then it seems to smooth out. Seems like it's starving for fuel. I pulled a plug and it's completly black so I need to get this all sorted out.

    And I believe it is one of the cheapo liquid filled gauges.
     
    Last edited: Apr 11, 2015

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