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Can a Boat Plow Snow?

Discussion in 'Chevy Trucks' started by owen, Aug 8, 2004.

  1. owen

    owen Member
    from florida
    Messages: 34

    I have found that you guys are the experts on 454s so maybe you can help with my boat.

    Under a load when I hit about 3000 RPM it boggs down like the choke is on. If I hold the large butterfly valve on the carb CLOSED it will get to 3500 RPM before bogging down. If I open that large butterfly valve at any time it boggs down.

    This is late 80s to early 90s 454 rated at 330 hp and 4600 RPM with a Rochester 4MV 4bbl Carb.

    Also I seem to have a intake manifold leak. It is blowing though. I figured that would suck:confused: Right where the choke heat thing is beside the carb if the manifold is wet it makes bubbles.:help:


    BTW, when I'm sitting in 80 degree water off the Bahamas this winter I will be thinking about plowing snow:D
  2. Tommy10plows

    Tommy10plows Senior Member
    Messages: 345

    What engine manufacturer, fresh or salt water cooled? Delco, Prestolite, or mallory distributor?

    There are a few things that come to mind. First is how is the electrical system - plug wires, plugs, distributor cap, rotor, coil tower- any sign of green corrosion on these? Go down into your bilge. Check the wires when warm with an ohm meter, any exceptionally high should be replaced. In the middle of the night, run your engine in pitch black light and see if you can see any of your spark plug wires arcing, that is easy to check.

    Check your ignition timing, too far advanced could cause a pre-ignition condition.

    Next, put a vacuum gauge on the motor. Check for vacuum at idle, should be 17 - 19 inches. any pulsations indicate a leaking valve. Run the motor up slowly in rpms and watch what the guage does. Run it up to 2000, 2500, 3000, 3500, etc. and watch the behavior of the vacuum gauge. It will tell you if you are losing vacuum, a lean burn condition which can cause damge to your valves.

    Resist the temtation to blame the Qjet until you run through your electrical system check.

    Let me know what you find and I will suggest more.
  3. owen

    owen Member
    from florida
    Messages: 34

    thanks for all the HOMEWORK you gave me:)

    It's a closed system (fresh) cooled mercruiser. Don't know about the distributor.

    I'll get back when I know more stuff. Thanks for giving me a direction to head. I wasn't even thinking electrical & vacuum.
  4. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    leak is leaking from the exhaust passage or so it sounds.

    So when you artificial richen it it gets better? There may be other vaccume leaks that i would look for around the manifold or carb. I prefer to use propane to look for leaks, using either or starting fluid can work but I fear it ignighting.
  5. owen

    owen Member
    from florida
    Messages: 34

    There is fresh engine oil around the area of suspected leaking. Possibly coolant also.

    Where's the best place to hook up the vacuum guage? I've never even done it before, but I'm going to.

    How do find leaks with propane? Are you just smelling them?
  6. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    Fire up the motor, turn on a propane torch(not lite, just puking gas) and start moving it around areas of a suspected leak. Listen for changes in the motor, when the propan gets sucked into the motor via the leak it will alter how the motor runs. Maybe just a very small amount.

    Also look for dissconected or rotting lines for vaccume running off the motor some were(dont know what kinda vaccume stuff comes off a boat)

    So when you hold the secondarys closed it runs better? Or when you hold the choke closed? Or are you shure witch is witch?(no offense ment) Choke is on top of the carbkinda raised up in that funky riser thingy.
  7. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    What do the plugs look like?
  8. Mebes

    Mebes Senior Member
    Messages: 451

    You can spray carb cleaner around the manifold and carburetor area to find those vacuum leaks also, as an alternative to propane or ether.

    When you spray it near the vacuum leak the idle will raise .
  9. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    Yup, I've used it, but you really need to be carefull. Propane is pretty hard to screw up, that why I recomend it.

    Dont do this on a diesel though:eek: forgot to mention that, real easy for it to get away from you.
  10. Big Nate's Plowing

    Big Nate's Plowing PlowSite.com Addict
    Messages: 1,266

    not with the small ammount of gas from a soldering torch :rolleyes: maybe if you use a cutting torch it might produce enough to make it take off..... also why would you check for a vaccume leak on a diesel? they dont have a throttle butterfly to create it

  11. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    well not so much vaccum:eek: looking to see if there are leaks before the turbo(or I guess on a na anywere on the intake). Youll find if you have a leaky boot or something pretty quick. not really usefull in most cases and I dont think a propane torch would cause her to really go high but a little bit of either or carb cleaner goes a long way on a diesel. I searched to see if a line was leaky on a stroke once(the only time I have used it) and didnt get any change....I assumed I would so I assume since I got no change it wasnt leaking? Maybe my thinking was off? I was carefull not to hose around were the intake was sucking for fear of it running away. Duno if I was right or wrong? I may be a dumbass:eek:
  12. owen

    owen Member
    from florida
    Messages: 34

    Yes, when I hold the secondary air valve closed it runs better (not choke)

    I checked the ignition timing. It was off the scale. Probably like 20 degrees BTDC.

    I set the timing to the Mercruiser manual spec of 8 degrees BTDC at 800 RPM.

    All that is on top of this manifold is a distributor, coil, carb and thermostat, which the housing is leaking. I've put a new gasket in twice and no luck. The only rubber hose on it goes from the carb to the actuator that moves the secondary air valve on the carb..........................I see no where to hook up my vacuum gauge.:dizzy:

    Plugs look good to slightly rich burning.
  13. owen

    owen Member
    from florida
    Messages: 34

    Big Discovery.

    While doing my carb rebuild I noticed I have no IDLE VENT VALVE. Just two holes there on the back of the carb right by the accelerator plunger.

    Could this be kepping it from going over 3000 RPM????

    Can I just plug them or do I need to buy the part?
  14. Robhollar

    Robhollar Senior Member
    Messages: 766

    dont forget to check your fuel pressure, but your prob rite for looking for a vac leak....Rob
  15. A&M Snowplowing

    A&M Snowplowing Senior Member
    Messages: 119

    I have a 454 in my 27 foot IMP with a Bravo 1 outdrive. I had the same problem. My problem was there was water in the fuel. So pull the fuel filter and check it.
  16. rusty gmc

    rusty gmc Junior Member
    from maine
    Messages: 23

    check your prop size