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ignition/

  1. #1
    Senior Member partycattin's Avatar
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    Default ignition/

    I have a 1996 7.4.
    I noticed the motor was missing/popping last year so I changed the plugs and wires, cap and rotor. That didn't seem to solve the problem.
    We're out on our first trip and the boat ran great the first day out but started doing the same thing on the second day. We could hear the motor
    popping on the left side so I changed the 1,3,5,7 plugs. They were all slightly rich and the 7 was very rich.
    With the new plugs, it ran better for a half day and then got worse. Today my top speed went from 45 down to 30-35 with a lot of popping/missing while the motor is under a load.

    Thoughts on what could be the cause?

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  3. #2
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    Default

    Are you running a carb, or fuel injection?



    Darrell.
    San Diego.

    28ft Sportcat
    With Twins

  4. #3
    Senior Member partycattin's Avatar
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    whoops.
    Motor is carbed. Holley DP. It has Imco Powerflows and a K&N filter. Other than that, it's stock.

    Motor was opened up a few years ago due to an impeller problem. Heads were sent out to be checked and I believe they did a valve job on them. The Imco's were added at that time.
    Motor has been hard starting since then but did not have any problems with missing/popping until last year.
    It usually turns about 4900 rpm at wot and trimmed up. Less now that it's acting up.
    I've read other post that suggest a leak down test. Not sure if that is something to start with. I've never done one before but after doing research, it doesn't seem to difficult.

    Any help/ideas are appreciated.

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    Senior Member bordsmnj's Avatar
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    do you know how to check float bowl levels? sounds like a carb thing/ fuel delivery. but i'm just guessing -Jas
    Quote Originally Posted by Rep. Joe Wilson (R) View Post
    YOU LIE!!!!!


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    Senior Member partycattin's Avatar
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    Quote Originally Posted by bordsmnj View Post
    do you know how to check float bowl levels? sounds like a carb thing/ fuel delivery. but i'm just guessing -Jas
    We checked the float level last season when I first started having problems. It was ok. Also through in a new power valve.

    Would that make 1 cylinder continue to foul/gunk up a plug?

  8. #6
    Senior Member H20MOFO's Avatar
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    Burnt valve? Compression check maybe.
    Another Hot Boat refugee

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    ... Some Kind Of Monster's Avatar
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    What's your fuel pressure?

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    Cantard 71hallett's Avatar
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    Quote Originally Posted by H20MOFO View Post
    Burnt valve? Compression check maybe.
    x2
    Quote Originally Posted by gn7 View Post
    It would be a balmy 85* in Steel's shop if he would move a little faster

  11. #9
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    Default Where?

    Quote Originally Posted by partycattin View Post
    We checked the float level last season when I first started having problems. It was ok. Also through in a new power valve.

    Would that make 1 cylinder continue to foul/gunk up a plug?
    Where were you boating last, and where are you now? If an engine is getting more fuel than the air available it will pop unburnt fuel in the exhaust. IF you're super rich the excess fuel CAN puddle up in the floor of the plenium and drain into the back runners, or runner, if it is a dual plane intake. Is #7 the lowest runner?............Just an idea...MP
    LOUD BOATS SAVE LIVES

  12. #10
    Senior Member partycattin's Avatar
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    Quote Originally Posted by Moneypit View Post
    Where were you boating last, and where are you now? If an engine is getting more fuel than the air available it will pop unburnt fuel in the exhaust. IF you're super rich the excess fuel CAN puddle up in the floor of the plenium and drain into the back runners, or runner, if it is a dual plane intake. Is #7 the lowest runner?............Just an idea...MP
    I was having the problem last year at Mojave, Havasu, and Lake San Antonio.

    The intake is stock Mercruiser. Not sure if it's single or dual plane.
    Carb is not stock. Maybe it's to big for the motor.

  13. #11
    Senior Member partycattin's Avatar
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    Default Twist

    Ok, here's a twist.
    Saturday we went from Havasu to Park Moabi. Boat was spitting a lost and not running at full power. We cruised up there and did not push it to hard. Sat at Park Moabi most of the day with a quick cruise to the store to get the kids Ice cream.

    We left Park Moabi after being there 5-6 hours and on the way back, the boat ran great.

    One thing I have been noticing is that my amp guage is sometimes at 9-10. On the way back down river when it was running good, the amp guage was showing 13-14 amps. I'm wondering if I have a bad connection or an alternator that is on it's way out and maybe not allowing my ignition system to get enough juice????

    Thoughts?

    I think I may do a leak down test this week just to see if anything shows up. Also will check the alternator.

    Thanks again for the suggestions.

  14. #12
    Seriously off center slowride's Avatar
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    SOunds like your ignition is sensitive to low voltage.






  15. #13
    Some guys never learn. bocco's Avatar
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    I had a case with Mercruiser ignition where the boat started fine and ran OK but it popped under hard load only. It turned out to be the coil. As soon as I pulled the coil wire out of the coil I could see it was burned.

  16. #14
    cfm
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    I'm taking it 'amps' was really meant as 'volts.'

    All ignitions are sensitive to alternator/batteries since ignitions are electric devices that run off those.

    Get your alternator/battery/and or electrical woes work'd out before you start throwing parts at the wrong area.

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