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Lost prime in stbd motor

Discussion in 'Technical Discussion' started by g collis, Jun 2, 2016.

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  1. g collis, Jun 2, 2016
    #1
    g collis

    g collis Member

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    I know it's in here somewhere, just can't find it. My motors are DD 12v71TI's. Changed the racors and secondary filters on both engines. Port fired right up and runs like it should. Stbd, not so lucky. She fired, started missing and gasping. Lost her prime.

    So, how the heck do I get her re-primed and bled?????
  2. CaptPKilbride, Jun 2, 2016
    #2
    CaptPKilbride

    CaptPKilbride Senior Member

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    Is there a priming pump, either manual or electric, in your fuel system?
    Make sure you re-opened all the fuel valves. Check the racors make sure they are full.
    Use the priming pump to bleed the fuel system starting with racors, then secondaries, then anyplace else there is a bleed screw.
  3. g collis, Jun 2, 2016
    #3
    g collis

    g collis Member

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    Unfortunately there is no priming pump on these old girls. Racors are full, but I think I'll pull the secondary and double check it.
  4. Pascal, Jun 2, 2016
    #4
    Pascal

    Pascal Senior Member

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    On my 8v71 I once lost prime and used a manual brass oil change pump to reprime. I hooked up the intake (bottom) to the primary outlet, and the outlet of the pump to the line going to the engine. Pumping it a few times was enough to pull enough fuel thru the Racor and into the engine mounted secondary.

    Once you get these DDs running, even badly, they will self bleed in a couple of minutes

    Without a pump, the engine pump will eventually pull fuel but that's a lot of wear on the starter.
  5. g collis, Jun 2, 2016
    #5
    g collis

    g collis Member

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    Got her running. Secondary filter wasn't full enough. Top it off and pow she runs.
  6. CaptPKilbride, Jun 3, 2016
    #6
    CaptPKilbride

    CaptPKilbride Senior Member

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  7. g collis, Jun 3, 2016
    #7
    g collis

    g collis Member

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  8. Lepke, Jun 3, 2016
    #8
    Lepke

    Lepke Member

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    Usually getting the Racor full and filling the secondary filter is enough to get a dry DD running. My Racors are below my day tank so gravity will fill them. I have inline electric pumps installed that the normal fuel pump can pull thru. When the fuel system has been opened, it makes it easy to bleed the system and save starter wear. Also a gauge after the secondary so at a glance I can see if the injectors are getting fuel. It comes from a fuel problem I was trying to figure out when I was a boy.
  9. g collis, Jun 4, 2016
    #9
    g collis

    g collis Member

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    Great idea about putting the gauge in after the secondary.
  10. Capt J, Jun 8, 2016
    #10
    Capt J

    Capt J Senior Member

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    I have NEVER had to use a priming pump to prime air locked Detroits, ever. Usually try turning over, if airlocked, close valves, top off secondary, top off racors, open valves, advance throttle halfway turn over for 20 seconds and they'll start on a few cylinders, after about 20 seconds they'll start working the air through and accelerating, have hand on throttle and keep bringing it back and keep them around 1000 rpms.
  11. CaptPKilbride, Jun 8, 2016
    #11
    CaptPKilbride

    CaptPKilbride Senior Member

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    I like priming pumps because they make it easier to top off the racors and secondaries.
  12. bernd1972, Jun 19, 2016
    #12
    bernd1972

    bernd1972 Senior Member

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    Don´t forget to check the fuel lines. There is most often a reason for useless air in the fuel system and you don´t want to play that game again and again or even experience an engine fail when needed because of a technically minor issue...
  13. P46-Curaçao, Jun 19, 2016
    #13
    P46-Curaçao

    P46-Curaçao Senior Member

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    My Detroit mechanic (36 years of experience) just came on board when I read this article...

    FYI, he confirmed Capt J his opinion... and now drinks his (first) whiskey and waits for his family so I can take them out to celebrate "Fathers day"!
  14. Capt J, Jun 19, 2016
    #14
    Capt J

    Capt J Senior Member

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    One time I had an issue with Detroits losing prime and it ended up being those priming pumps that are about the size of a soda can (touch larger). They have plastic check valves with a spring in them and they went bad allowing air to enter the system.