Tunning Question
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Tunning Question

  1. #1
    Member CashLeak's Avatar
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    Default Tunning Question

    I have a friend that bought my 78 Spectra 20 with a BBF 460 and a stock Berkley JC pump. He over heated it and blew the head gasket He took it to another friend of his and they pulled the heads replaced the gaskets and decided to put another cam and lifters in it now the boat will not turn over 3500 rpms its hard to start Its burning really lean It even chewed the bendex out of the starter. Of course his buddy that did the work is blowing him off and telling him it needs a bigger carb. His buddy knows nothing about jet boats and I think its a huge mistake to swap out the cam not knowing how the rest of the motor is built. When I owned the boat it had a stock hardin marine 460. This is what I know about what was done. The new cam is a comp cam with .3060 lift and 230 duration lobe separation 110.0 Not sure if it was set up with a 4 deg advance or retard. Its running a holley 750 dbl pumper with 70 primary jets and 73 secondary jets a stock spread bore intake It has a Mallory electronic dist The pump is a stock Berkley with a aluminum impeller. Im trying to keep my friend interested in jet boats nothing is worse than a boat that doesn't run so any help would be appreciated Below is a pic of the boat when I owned it
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  3. #2
    gn7
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    Depending on how much time is on this thing. he needs to see if his cam is still a cam. Flat lobes can make the cranking compression go thru the roof.



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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by gn7 View Post
    Depending on how much time is on this thing. he needs to see if his cam is still a cam. Flat lobes can make the cranking compression go thru the roof.

    That was my first thought too..

    Also if the cam is retarded it wont be able to get out of it's own way... Compression check, measure the cam lobes via the push rods, check valve timing, the list is virtually endless.

    Should be able to sort it out if the platform is sound (cylinders, valves etc.).
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    A Real Love For Speed Bass Lake Boz's Avatar
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    Default Tuning Question?

    As GN7 Asked, How long has the engine been run since the repair?
    IF this was my decision I would Re-check the whole job.
    Do a cylinder leak down test. If it got hot it may have ring & or piston damage affecting compression and performance.
    Check the cam that had come out as to the actual condition and specs.
    At the very minimum you can measure the lobe lift.
    Then degree the cam. You should be able to mount a degree wheel by just removing the balancer and be able to check if the cam is within a couple of degrees of listed cam lobe timing. If it is not then that is where you need to start. If the cam is installed correctly then you have ruled this out.
    The starter issue was self inflected by advancing the timing to get the thing to start and run, Well it’s barely running from the sounds of it.
    From here this is my first thoughts on this.
    Please keep us posted on the progress and the outcome.
    Good Luck.
    Last edited by Bass Lake Boz; 05-27-2013 at 11:58 PM.

  7. #5
    gn7
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    Quote Originally Posted by GT Jets View Post
    That was my first thought too..

    Also if the cam is retarded it wont be able to get out of it's own way... Compression check, measure the cam lobes via the push rods, check valve timing, the list is virtually endless.

    Should be able to sort it out if the platform is sound (cylinders, valves etc.).
    Almost all Comp Cams are ground 4* advanced, Its a trademark of theirs. Even with an emissions timing gear set the timing will be close to straight up. But with worn lobes the closing intake is so soon that it makes the cranking pressure shy rocket. Intake opening, and the exhaust lobes have little to do with cranking pressures, but the early intake closing will really change the cranking pressures.

    If the cam was retared it would kill the performance, but the cranking pressures would be lower.

    Once the engine starts, the short timing and low lift of worn cam make it gutless.



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    Living in a cage of fear thatguy's Avatar
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    All of that plus was the timing set replaced?

    If it did all that from the word go the timing set could be installed WAY off if it is a multi- position set.
    Either way it sounds like a hot mess and needs to start being dissassembled, IMO.
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    Led
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    being that it has overheated, surely the timing chain wasnt junk, i would pull the valve covers, roll motor over and make sure all rockers are moving all the way up and down, a flat lobe will be noticeable, if they are OK, i would check valve lash, if they are too tight...the cam is on it way out and can cause the hard cranking, pull the plugs and see how it cranks also

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    ​dumb question but did anyone check the push rods?

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    Cam is new lifters are new chain and gears are new Cam was broke in on the trailer I think Its down to timing and the carb So givin the lift and duration of the cam is a 750 holley enough to run that motor or do we need to go bigger ???

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    Cams can go flat quick especially if their new..............................

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    gn7
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    Quote Originally Posted by CashLeak View Post
    Cam is new lifters are new chain and gears are new Cam was broke in on the trailer I think Its down to timing and the carb So givin the lift and duration of the cam is a 750 holley enough to run that motor or do we need to go bigger ???
    You have plenty of carb. The fact that the cam is new is what sets of the alarm.



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    Hard starts would make me think timing, for a cruiser, I would set timing for mild tune, easy start and restart

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    What caused it to overheat? Is there an issue with the pump? I'd check it out, minimally, to make sure it's not binding up/seizing internally.

    Quote Originally Posted by gn7 View Post
    You have plenty of carb. The fact that the cam is new is what sets of the alarm.
    OP, this is good advice. New flat tappet cams are pretty well known to occasionally go flat shortly after break-in. It happens. Pretty easy to spot if you take the valve covers off and give it a spin. Pull the plugs when you do this. It's usually only a couple lobes, so you may see a couple valves not opening as much as the others. Could even be only one, so make sure to look closely at each while comparing it to another. As gn7 and others have mentioned, it would explain hard starts and no power.

    And, a 750DP is a good choice. Tell him not to waste his money.

  16. #14
    Member CashLeak's Avatar
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    Default update

    Turns out the cam is flat . His engine builder (a friend of his) used the wrong valve springs. Now the motors coming out of the boat for a complete rebuild. For him I think its a lesson learned just because your buddy has 20s on his truck doent mean he knows how to build a motor !!! He has the Engine at a real builders shop someone who know how to read a cam card !!!

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