1978 Johnson Seahorse 70HP Qestions?

Discussion in 'Outboards' started by Traxxasmaxx, Jun 9, 2010.

  1. capt littlelegs
    Joined: Apr 2010
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    Location: England

    capt littlelegs New Member

    He's done this before! :)
  2. Traxxasmaxx
    Joined: Jun 2010
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    Location: Florida Gulf Coast

    Traxxasmaxx 1978 Johnson Seahorse

    Good Stuff

    Hey thanks dustycrockett. I am taking her out tomorrow and will be buying som plugs in the morning. So that number really helps. Just out of curiosity last time I took it out for some dumb reason I didnt let it warm up. At full throttle it just wouldnt go, but then out of no where it would take off. I was thinking I might have fouled a plug and when it got fire it would run like normal. Maybe its a coil though. The guy I bought it off used it everyday to check his crab traps and never had this problem but he always let it warm up first. Today I put it in a dunk tank and when in neutral it runs and revs like a champ. No delays in throttle response. When I take it out tomorrow if it has the same problem even after I let it warm up any ideas as to what it could be?

  3. dustycrockett
    Joined: Jun 2010
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    Location: Texas

    dustycrockett Junior Member

    yeah it'll do that cold -- did it get better after it warmed up?

    If not, bogging like that is a classic symptom of dirty carbs but it could be a number of things. I always do a compression and spark test first. Compression should be about the same on all 3 (within 5 or 7%), anything upwards of 100 would be ok, I'd expect around 120. Spark should jump a 7/16" gap on an inline tester clipped to the block. Inspect the fuel tank for water & debris. Make sure the fuel line holds pressure.

    If it bogs, but you can nurse it up to WOT, check to make sure the throttle cam hits the roller right on the mark, and the timer base moves smoothly to its stop without sticking when you advance the throttle (see attached -- that's a mid-eighties model, but all the parts are there). Those plastic fittings holding the throttle/spark rods in place, they only last 29 years or so before they start breaking up, and you'll get some weird symptoms.

    Running in a tank isn't a good test of how it'll perform under load. In neutral, it can sound surprisingly good on 2 cylinders.

    I have one of those but its a '79 vintage evinrude -- virtually the same motor. In spite of having no formal mechanic training I've never put it in the shop. Get yourself a shop manual. There's really not much can go wrong with this motor that you can't fix yourself. I highly recommend the factory manual, www.iboats.com or www.kencook.com or www.marineengine.com all have it. Will pay for itself many times over.

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