470 Merc getting fuel,spark and good compression but will not stay started

Discussion in 'Sterndrives' started by spradlin, Jun 14, 2009.

  1. spradlin
    Joined: Jun 2009
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: ohio

    spradlin New Member

    I have a 1982 470 Merc. It was updated with a marine alt last year and we have never had a problem out of her. We are getting spark,fuel and we have good compression. When the starter is engaged and I hold the key it acts like it is running while the starter is engaging the fly wheel. When I let the key go it simple dies. I've always heard that you need spark, fuel and compression to run and I have all three! I'm stumped. Could the battery need replaced even though it cranks well?
     
  2. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Yes, you need these 3 for an engine to run, but the amount of fuel vs. the amount of air and the timing of the spark can also spoil the fun.
    Check the timing and look for clogged jets!
     
  3. spradlin
    Joined: Jun 2009
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: ohio

    spradlin New Member

    Reply to CDK

    Timing seems fine and the jets are clear. Changed the ignition switch just in case it was the switch. Still acting the same way. I will replace the distrib cap and rotar to take a shot in the dark. Thanks
     

  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    There is a bypass at the starter to the ignition. It get power when you are cranking and will fire the engine. When you let go of the key, the power goes from the I terminal that has a ballast inline. The ignition switch is bad or the purple wire is broker or disconnected.
     
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