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Thread: Mercruiser carby issue. I need help, info

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    Default Mercruiser carby issue. I need help, info

    Not strictly auto, tho close. I'm working on a 3 Litre boat motor & found that covering the carby throat didn't make a damn bit of difference to the motors rev's added to that it didn't try to suck my hand into it. It idles a little rough though not bad. There's no obvious mixture screw so can't alter that. So were the hell is it getting it's air from?? The Mercruiser alpha 1 is a 2002 4 cyl electronic ignition model. Googl ing I didn't find any reference to this problem. I've little to no experience with Mercruisers, though it's only a small truck engine marinised as far as I know.



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    hop over to either

    thehulltruth or

    they would be more able to help

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    Pm Rick, he used to work on boats....

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    Finally got FTTN, 710m line length....

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    suggest you get down on your knees and look under intake manifold and you will see a big hole ????
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    2 stroke issues can be tricky to diagnose. if its not sucking air it might be a reed valve issue or a compression issue with that cylinder. peek inside the bore with a borescope.

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    Quote Originally Posted by hinekadon View Post
    suggest you get down on your knees and look under intake manifold and you will see a big hole ????
    Can't, it total enclosed jacket (heat exchanger, includes exhaust manifold).

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    Quote Originally Posted by VroomVroom View Post
    2 stroke issues can be tricky to diagnose. if its not sucking air it might be a reed valve issue or a compression issue with that cylinder. peek inside the bore with a borescope.
    Sorry meant to include, it's an inboard 4 stroke

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    Oh !one of those so you have to remove the manifold and find the crack on the edge of the flange ?Is it a totally cast one ?
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    Quote Originally Posted by hinekadon View Post
    Oh !one of those so you have to remove the manifold and find the crack on the edge of the flange ?Is it a totally cast one ?
    Yeah totally cast & enclosed in a water jacket

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    yep some of the studs will be a pain in the butt but a bit of heat is the way to go , it is easier to just buy a new one then you can smash off the old one but they can be repaired if you have welding skills . They have to be cut apart welded and rewelded back together the hole can normally be seen thru the intake ports , if you take out the spark plugs the cleanest one will be where the hole is as it nornally sucks water in as well but that dont help you much any way other than to prove the theory cheers don whats the horsepower ??
    Last edited by hinekadon; 06-04-19 at 12:11 PM. Reason: more
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    If the intake manifold sucked water into the cylinders then that motor would be toast at least if it was a gaping hole.
    A very small crack might have been survivable but hardly visible.
    Maybe it is just the seal of the intake to the carby somewhere that leaky. IMO more likely and an easy fix.
    Also check if it has some vacuum hoses that are cracked or leaky.
    Last edited by Uncle Fester; 10-04-19 at 10:37 PM.
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