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Thread: Fuel starvation

  1. #1
    Join Date
    Oct 2001
    Location
    High Wycombe, Bucks.
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    71

    Fuel starvation

    I have recently had a return fuel line fitted to my Cobra -
    i.e. a re-circulating system. I am running a Holley 700 Double Pumper and the fuel pressure was originally set at 6 psi. However, since it has been fitted, I noticed it ran out of "go" at around 4800 rpm. So, we increased the fuel pressure to 9.5 psi and it improved things slightly as now it would run to 5300 rpm before it felt like it was hitting a rev. limiter. Increased it again to 11 psi and it is no better.
    Am I overlooking anything obvious and has anyone had these problems because I think 11 psi is too high for a Holley carb.?

    Simon.

  2. #2
    Join Date
    Jan 1999
    Location
    Northampton, Northampton, UK.
    Posts
    9,180

    RE: Fuel starvation

    A holley carb should be able to run 600hp on a 750cfm carb on a constant pressure of 6psi with no problems whatsoever.

    Which electric pump and regulator are you using?

    Best Regards

    Robert
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    Best Regards

    Robert

    Crossed over for a while - Overlanding - Some people are just like slinkies, they don't really have a purpose but they still bring a smile to your face when you push them down the stairs.

  3. #3
    Join Date
    Oct 2001
    Location
    High Wycombe, Bucks.
    Posts
    71

    RE: Fuel starvation

    Robert,

    I agree with you it shouldn't need to exceed more than 6 psi fuel pressure.

    I am running a Holley Blue Top 802 electric fuel pump which is more than up to the job. The setup as I understand it (I didn't fit it) is fuel goes from the tank through 2 small filters and then into a large Fram HPG-1 filter, then to the Holley carb. then through a restrictor back to the tank.

    Before the re-circulating system was fitted it was the same as above except; after the Fram filter the petrol passed through a regulator which was supplied with the Holley Blue Top fuel pump. Thus the difference is the regulator has gone and an additional line is being run back to the tank with a restrictor in it. I didn't have any problems before the new bits were fitted?

    Help?

    Simon

  4. #4
    Join Date
    Jan 1999
    Location
    Northampton, Northampton, UK.
    Posts
    9,180

    RE: Fuel starvation

    The Holley Blue has an internal regulator - Holley pumps have rotary sliding vanes and have replaceable parts including filters. The higher performance H802 pump is sold with a regulator whereas the H801 has sufficiently low pressure not to need one in most applications.

    Are the two small filters restricting flow, and what size fuel line are you using?

    Robert
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    Best Regards

    Robert

    Crossed over for a while - Overlanding - Some people are just like slinkies, they don't really have a purpose but they still bring a smile to your face when you push them down the stairs.

  5. #5
    Join Date
    Oct 2001
    Location
    High Wycombe, Bucks.
    Posts
    71

    RE: Fuel starvation

    Robert,

    I see what you are getting at, but the two small filters and same size fuel line (can't remember the size, but it is as Holley recommend in their catalogue) are being used as before when everything was fine. Looking at what has changed, the problem must be linked to the restrictor in the return line or the fuel line itself? Or maybe not???

    Simon

  6. #6
    Join Date
    Jan 1999
    Location
    Northampton, Northampton, UK.
    Posts
    9,180

    RE: Fuel starvation

    It might be holley recommended, but does it have the correct flow for the HP output of your engine?

    You might be right in respect to the return feed, what sort of restrictor is it? What size is the fuel feed and return?

    Robert
    Forum Admin

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    Best Regards

    Robert

    Crossed over for a while - Overlanding - Some people are just like slinkies, they don't really have a purpose but they still bring a smile to your face when you push them down the stairs.

  7. #7
    Join Date
    Feb 2007
    Location
    Bradford, West Yorkshire, England.
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    RE: Fuel starvation

    Dont really know what I'm talking about (no I dont mean generall wilf) so please excuse me if this is incorrect. Is it not that the return line is only used for fuel injection systems that use roller vane fuel pumps delivering around 60 psi and up to 140 psi. If this is the case is iy not that a return pipe will have the effect of srarving the pump as the limited pressure even at 9 psi will not come close to pressurising the fuel delivery system. If this is so take off the the return pipe and use a fuel regulator to set pressure. The setting you require is between 5 and 7 psi. Recommendation is 7 psi at idle and maximum 4 psi at engine redline. Do not go over 7 psi or you will get fuel passing the needles and squirting out of the fuel bowl vent.

    Whilst you are at it do yourself and the engine a favour. Sell the double pumper as it will save you fuel costs and give no less performance other than for stop start full throttle acceleration. More important it will avoid you getting unbelievable cylinder wall wear caused by cylinder washdown due to the unbelievably oversized accelerator pump jets. In extreme cases wear can occur in as little as 5000 to 10000 miles. So either use a very light foot or get a heavy wallet.
    Mike.



  8. #8
    Join Date
    Feb 2007
    Location
    Bradford, West Yorkshire, England.
    Age
    65
    Posts
    2,266

    RE: Fuel starvation

    Dont really know what I'm talking about (no I dont mean generall wilf) so please excuse me if this is incorrect. Is it not that the return line is only used for fuel injection systems that use roller vane fuel pumps delivering around 60 psi and up to 140 psi. If this is the case is iy not that a return pipe will have the effect of srarving the pump as the limited pressure even at 9 psi will not come close to pressurising the fuel delivery system. If this is so take off the the return pipe and use a fuel regulator to set pressure. The setting you require is between 5 and 7 psi. Recommendation is 7 psi at idle and maximum 4 psi at engine redline. Do not go over 7 psi or you will get fuel passing the needles and squirting out of the fuel bowl vent.

    Whilst you are at it do yourself and the engine a favour. Sell the double pumper as it will save you fuel costs and give no less performance other than for stop start full throttle acceleration. More important it will avoid you getting unbelievable cylinder wall wear caused by cylinder washdown due to the unbelievably oversized accelerator pump jets. In extreme cases wear can occur in as little as 5000 to 10000 miles. So either use a very light foot or get a heavy wallet.
    Mike.

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