455 olds jetboat problems
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455 olds jetboat problems

  1. #1
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    Default 455 olds jetboat problems

    Hello,I am new to this forum and need some help from someone who has more knowledge of olds 455 than I.I just recently rebuild my brothers 455 olds,it is a 1973 Sidewinder super jet with berkley pump (19')He has owned the boat since new and arround 10 years ago lost oil pressure and spun a bearing.He finally decided to have me do a rebuild on it and this is what was done.Napa did machine work,did not need boring ,block was OK.Turned crank,rebuilt 3 rods,cleaned and rebuilt heads to stock spec's.Basically it is a stock block and heads.Block is a Fa,heads are a Ka.Put a Mallory marine breakerless distributor,comp cams 268H cam and timing set,stock manifold and I rebuild factory rochester carb.Problem is the motor used to turn 4800 rpm's now it dies at 4200.Also when I open engine compartment when it is ideling the rpm's increase 200 rpms.Timing is set at 14 at idle.Not sure if it is carb,vacuum leak,fuel pump or what.Just don't no what to try first.Any help would be much appreciated.Thanks

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    Default Air??

    Boy, that is some tight fitting hatch if it's truly starving the engine for air. Have you tried running the boat without the hatch???? Be SURE to run the blower(s) before starting if that hatch fits that tight....... Check out the fuel delivery system. The boat has been sitting and fuel lines do rot/crack and suck air..... Ray
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    Quote Originally Posted by Moneypit View Post
    Boy, that is some tight fitting hatch if it's truly starving the engine for air.
    That, and/or the air that does make it's way in there... gets VERY HOT?

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    Horsepower sells Engines lefty's pride's Avatar
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    ya that 200 rpm on the opening of the hatch scares me there should be enough venting that it would not make a diffrence. but why did it not do that before? does it even have a blower? when it gains the 200 rpm is the blower on? i would totally try running it with the hood off.
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    There is a hole in the cover right in front of the flame arrestor where it gets fresh air.Looks like a little scoop.Never did this before.Fuel lines are original,run to the front to tank.Also had a hard time finding a fuel pump,original pump had a clear tube which ran up to carb that had a piece of paper in it that said if this ever gets wet replace fuel pump.I used the old pump for the first trip and it ran good,didn't push it past 3000 since everything was new but when I put it back in shop there was fuel in that clear line.Couldn't find a new marine pump with that fitting on it anymore so just bought a fuel pump from advance auto.Only problem is it has 5/16 outlet where old one had 3/8.Could that make that much difference?Also sitting in water if I rock the boat from side to side the rpm's change.Have run it with out cover and no change.Thanks for your help.

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    Yes it has a blower,but it will do this sitting in shop in the morning when in is 70 degrees.I just seem to thank it has a major vacuum leak somewhere.

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    Default Liquid fuel

    Quote Originally Posted by JohnB View Post
    There is a hole in the cover right in front of the flame arrestor where it gets fresh air.Looks like a little scoop.Never did this before.Fuel lines are original,run to the front to tank.Also had a hard time finding a fuel pump,original pump had a clear tube which ran up to carb that had a piece of paper in it that said if this ever gets wet replace fuel pump.I used the old pump for the first trip and it ran good,didn't push it past 3000 since everything was new but when I put it back in shop there was fuel in that clear line.Couldn't find a new marine pump with that fitting on it anymore so just bought a fuel pump from advance auto.Only problem is it has 5/16 outlet where old one had 3/8.Could that make that much difference?Also sitting in water if I rock the boat from side to side the rpm's change.Have run it with out cover and no change.Thanks for your help.
    That part sounds like either the fuel in float bowl is sloshing around, OR it is so rich it is puddling fuel in the bottom of the plenum.... The rocking causes liquid fuel to run down to the valves......AND THAT sounds like a huge vacuum leak somewhere.......Air entering the intake without passing through the carb first leaving gas sitting around inside the intake runners.....Ray
    LOUD BOATS SAVE LIVES

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    what kind of intake gasket did you use? ii was reading on realoldspower.com and some gaskets are to thick some are to thin, seems to be a common problem. if the intake doesn't sit down just right it could have major air leaks..

    did you try spraying some carb cleaner around the intake gaskets, while the engine is running? if the idle raises, you found a leak
    Last edited by E Rock; 08-30-2010 at 09:37 PM.

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    Senior Member jetboatperformance's Avatar
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    May have missed this but does the engine simply "laydown" or does it bog and die and if it dies how quick can you get a relite ? also does it miss or cut out ? anybackfiring ? Tom

    (Hate to say it but the first thing that comes to mind is the Quadrajet )

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    The intake gasket was a one piece thin metal valley pan type gasket which required sealent arround the water passages.Motor runs along smooth at about 3000,than when I kick it wide open it hesitates just a bit but goes right to 4200 and thats it.Keeps running fine,no spitting or missing,just thats it.I bought a edelbrock 1410 marine carb yesterday but need adapter plate to install it but don't want to put that on if not sure it will fix it.Seems like it ran better the first time we took it out before we had to change fuel pump.I am thanking about going ahead and put a electric pump ,new fuel line and filter just so I will no it is getting enough fuel.Not sure what kind to get?Also now when I try to adjust the 2 idle air mixture screws it makes no difference when I turn them all the way in or out.This was my first quadrajet rebuild,maybe I screwed something up.But all I did is clean it and install new rebuild kit,not much to it.Thanks for the help.

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    I think putting that carb on would be very easy to see if that's your problem. Further, is the engine cover maybe pinching a fuel line or messing with the throttle cable? That part is the biggest mystery to me.

    As far as the 4200 RPM, doesn't seem too far off for a stock motor. Maybe you were getting a false reading from the old distributor. I get @4300 rpm on my stock 455 at WOT, my old tach used to read 4400.

    Oh, and i'll be the first on here to tell you, get rid of that metal turkey tray gasket.
    1992 Eliminator Daytona 21'

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    No pinched lines or throttle cable problems,the tach difference makes sense but the boat has always run 65 to 68 on smooth water now struggles to go 50.

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    Quote Originally Posted by JohnB View Post
    Problem is the motor used to turn 4800 rpm's now it dies at 4200.
    Quote Originally Posted by JohnB View Post
    the boat has always run 65 to 68 on smooth water now struggles to go 50.

    Something is not adding up. 600 RPM does not = 15 to 18 MPH.

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    I no,that is what is so frustrating,since having the boat since it was new I no how it should feel and how it should respond,just doesn't feel like it has the power it used to.I was hoping that the modern dist,new cam,10 quart oil pan,new plugs,wires,basically new everything it would run better than new.Just really frustrated now.I have spent more on rebuilding motor than boat cost new in 1973.Good thing is it still looks like new.

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