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Thread: Weird engine running problem

  1. #1
    Senior Member Einar Irgens's Avatar
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    Weird engine running problem

    New built 2.7 engine with Zenith tin 40s. Everything in order when at idle. After a couple of minutes drive it starts popping badly and deliveres power unevenly. Have checked all the usual parameters, no result. Seems that the problems occur as the engine gets hot. What ever could cause this?

    Einar

  2. #2
    Senior Member dirk07's Avatar
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    Einar,

    Which fuel pump and fuel piping from and to the tank do you use?

  3. #3
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    I would check that the air flow is balanced on each bank of the zeniths at about 3000 rpm.

  4. #4
    Senior Member Einar Irgens's Avatar
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    Quote Originally Posted by dirk07 View Post
    Einar,

    Which fuel pump and fuel piping from and to the tank do you use?
    The fuel pump connects thru a regulator that ensures a steady pressure of. 25 bar. Could still supply too little? The voltage regulator is no good. Voltage goes up to 16 V. Tried disconnecting it, but even with battery power only, failure mode was unchanged.

  5. #5
    Senior Member Einar Irgens's Avatar
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    Checked, balance ok. Keep in mind it runs fine before getting hot. I can't really picture any carb error conditions that are like that.

  6. #6
    Sounds like fuel filter in gas tank may be partially clogged. You can drive a little distance but fuel flow cannot keep up with demand. This can also be intermittent, I know this from a similar issue with my car.

    This assumes you have an early 911 with furl strainer ar the bottom rear that is inside the tank, it takes a 22mm (this is a guess about wrench size) wrench to remove the filter from the tank.
    Paul Abbott
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  7. #7
    Senior Member Einar Irgens's Avatar
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    Quote Originally Posted by 1QuickS View Post
    Sounds like fuel filter in gas tank may be partially clogged. You can drive a little distance but fuel flow cannot keep up with demand. This can also be intermittent, I know this from a similar issue with my car.

    This assumes you have an early 911 with furl strainer ar the bottom rear that is inside the tank, it takes a 22mm (this is a guess about wrench size) wrench to remove the filter from the tank.
    Paul,

    It's a '73. The fuel tank was new less than 10 years ago. However, as we checked and adjusted the ignition advarte, it ran empty. Unfortunately, I filled it up yesterday with 80 litres. Takes an effort to drain it, which I suppose must be done before checking the filter.

    Einar

  8. #8
    Senior Member Einar Irgens's Avatar
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    Could the CDI box be damaged from the high charge voltage? Is it more likely to fail at high engine load?

  9. #9
    Senior Member Einar Irgens's Avatar
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    Solved. Dirty points. I suddenly remembered that I experienced similar symptoms a couple of years ago. Important to make sure the gauges are clean before used to measuring the gap!
    Last edited by Einar Irgens; 09-24-2022 at 11:10 PM.

  10. #10
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    This is why I went to Pertronics to replace the points
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