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Thread: 6-71 full fuel

  1. #1

    Default 6-71 full fuel

    Hi all very new to this so bear with me
    i have a gray 6-71 that's been sitting in the bottom of a boat for about 8 years not touched so here is where it starts not knowing about detroits I put new fuel in it and hit the start button and away it went ( real hard) Anyway I got it shutdown and dived deeper pulled the rocker cover off and the fuel rail was stuck so I freed that up and now the fuel rack will not return to full fuel when shutdown so I have to throttle on to get it to start not very desireable in a boat and now idle is about 1800 rpm and if I Pull the stopper cable so it returns to idle not stopped just slowed it will stall or when released will rev back up again or stop. I have had the govener out and all is free so asking what to adjust to get it to run properly once I put the boat in gear and the motor has load it is fine just when I put it in nuteral it revs up and won't start without throttle ( and to throttle on it kicks the boat into gear not desirable any help would be appreciated thanks
    Last edited by Pigshead7469; 08-22-2017 at 11:18 AM.

  2. #2
    Join Date
    Nov 2009
    temecula, ca., usa

    Default Re: 6-71 full fuel

    Sorry you're having trouble.

    I'm not an in line 71 guy....6 and 8v71's were my bred n butter.

    But, the governor has two springs...low speed and high speed.

    It sounds as if your low speed spring may be run in too far.

    Look for a big hex on the side of the governor housing. That's the high speed spring adjustment. In the center of that hex is a screw with an Allen head and a jam nut threaded on to it. That is low speed spring adjustment.

    Loosen the jam nut and back out that screw a couple of turns and see what happens.

    I would advise, though, to make sure the emergency shut down is operable and that you or a helper can activate it quickly while you figure out what is going on.

    If the engine runs away and you can't stop it, it will self destruct and possibly injure you. They can punch holes in the hull and sink your boat at the dock too. It is serious business!
    But if the EStop works, you don't need to worry so address that first.

    Good luck and let us know what you find.

  3. #3

    Default Re: 6-71 full fuel

    Ok thanks for that I'll try that I was thinking all of the settings would be set as it was running ok when it got shut down all them years ago I'll give it a go and see what happens thanks again for steering me in the right direction cheers

  4. #4
    Join Date
    Nov 2009
    temecula, ca., usa

    Default Re: 6-71 full fuel

    Well, it's probably NOT that NOW that I know the REST of the story.
    I figured this was likely a recent purchase and somebody other than you had been screwing around with the governor.
    If it was simply shut down while running good it's probably a sticky problem due to corrosion.
    It could be the riser or the weights getting stuck. You need to pull the governor cover and check the travel on everything that moves.
    It might even clear up on it's own as you run it and oil gets thrown up there. But I wouldn't wait. Get in there and work and oil everything just as you did with the rack tube.
    Good luck.

  5. #5
    Join Date
    May 2015

    Default Re: 6-71 full fuel

    If you don't have a service manual, get one. They're often on Ebay. The WWII manual works for most Grays. Or join http://boatdiesel.com They have PDFs of early training and service manuals for 671s.
    If it was my engine, I would start from scratch, by the book. Or hire a Detroit mechanic to set the injectors and rack. High revs w/o a load will kill the engine.
    Ebay is a good place to find spares, too.

  6. #6

    Default Re: 6-71 full fuel

    change injectors call [email protected] [email protected]

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