Question about 1986 Ford F 350

3 Answers

I have a 1986 F-350 with a 460 in it. It runs strong when accelerating but rough when at a cruising speed. The vacuum line to the distributor is coming directly from the carb with no control valve in the line. Is it getting too much vacuum at cruising speed and actually running out of correct timing?

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  • imwhmo May 24, 2011

    The vacuum diagram shows a vacuum control valve (vacuum delay?) between the carb and the distributor. Do I need to find one?

  • imwhmo May 24, 2011

    I changed the vacuum line to the ported vacuum above the site hole on the carb and it reversed the issue. I think it is now a matter of checking the timing and readjusting the carb as the intermitent miss is now on acceleration. Thanks

  • imwhmo May 25, 2011

    After I switched the vacuum line to the ported outlet on the carb, it runs smooth at cruising speed but the eratic miss is there when accelerating. I think the rest is now adjusting the timing and readjusting the carb.

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3 Answers

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  • Ford Master
  • 3,018 Answers

  • If you put on a ported outlet already then adjust the carburetor.
  • Check them plugs and wires as well. Make sure they are doing you right. In fact a full tune up may be in order at this point.
  • Yea check the timing as well.
  • sounds like your just about there. I love older Fords. Can't beat them in my opinion.

Regards, Tony

Posted on May 25, 2011

  • Iron
    Iron May 27, 2011


    • Glad to be able to help.

    • Nothing beats an old Ford



    Regards,

    Tony

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  • Ford Master
  • 76,630 Answers

Hello
The vacuum line valve you speak of is just a delay valve and within a few seconds after reaching steady cruise the valve has allowed full vacuum to the distributor vacuum advance capsule so doubt that is the problem. I am a retired Ford dealer service technican and I was working for Ford when this truck was new and watched them age and saw the problems show up as the miles increased, here is what is the MOST common cause of any drivability issues with the 460 V8 equipped with the 4160 series 4 barrel carburetor, (which is a Holley designed carburetor), and that is the carburetor itself, the gaskets leak in the fuel metering plates on the front and rear barrels and dirt gets into the carburetor despite the fuel filter and causes lean fuel conditions and engine surge issues, also the vacuum controlled power valve leaks and causes surging, the cure is a quality rebuild of the carburetor, not a rebuilt unit from Kragen or Autozone, but someone who really knows this Holley designed carburetor and how to properly rebuild them, the book time is 5 hours to rebuild this carburetor correctly, and I've done perhaps a 100 of them. Also other problems with this engine are the intake gaskets leak and the EGR valve leaks at the valve pentile, this allows to much exhaust gas to enter the intake and causes surging as well, so have the intake checked for vacuum leakage and the EGR for proper operation. Also verify the ignitiopn timing is set to 10 deg BTDC.

Posted on May 24, 2011

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  • yadayada
    yadayada May 25, 2011

    When I answered this question I assumed you had set the basics like ignition timing.

  • yadayada
    yadayada May 25, 2011

    A misfire on acceleration would likely be spark plug cables. Carburetor adjustment will only affect idle and just off idle, so this is not likely to be your problem. If the spark plug wires are ok and not the problem then you still have a metering plate problem in the carburetor or a leaking power valve in the base of the carburetor. I know this engine and fuel delivery system like the back of my hand.

  • yadayada
    yadayada May 27, 2011

    Did you fix this without going through the carburetor?

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  • Master
  • 3,489 Answers

The carburretor may be leaking a little. The vacuum you need is "ported" vacuum. This means that vacuum is only applied when you are accelerating to aid in advancement of the timing. Whem at cruise there should be little to no vacuum. Centrifugal force (rotating force) will take care of needed advancement while at cruise. Try getting the proper vacuum hose on the distributor and take it for a test drive and let me know.

Posted on May 24, 2011

  • Kori Policy
    Kori Policy May 24, 2011

    Not for this. You can later if you happen to find one. For now just find ported vacuum and see how it drives.

  • Kori Policy
    Kori Policy May 25, 2011

    i would say so. It is also going to need to burn out some of the saturation and may require new plugs. Just simple MotorCraft plugs will do. Then adjust base/mechanical timing and then the carb for air/fuel ratio.

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