Chev 350 Inboard

Discussion in 'Gas Engines' started by mikealston2428, Apr 21, 2020.

  1. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Vacuum hoses tend to self seal under suction, you’ll seldom find them clamped unless they’re situated so that their weight will pull them loose from the barb.
     
  2. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Great thanks for clarifying that
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I suspect the boat was laden down with Marlin, and couldn't get on plane !
     
  4. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

  5. brendan gardam
    Joined: Feb 2020
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    Location: east gippsland australia

    brendan gardam Senior Member

    no, vacuum hoses just push on friction fit. if you are worried you can use small cable ties for a clamp.
     
  6. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Thanks Brendan,
    I've ordered new filters and a marine mechanical pump
    I've also decided to replace the spark plugs
    Once it all done I'll drop the boat in the water and see if problem sovled and I'll let you all know
    Thank You to all members that gave me advice
    This forum is fantastic I greatly appreciate the help
    Cheers
    Mike
     
    brendan gardam likes this.
  7. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    You're welcome Mike. Please let us know how you made out when you have time.
     
  8. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    I definitely will Missinginaction
     
  9. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Hi All,
    Just confirming clear tygon tubing is used for vacuum line from mechanical fuel pump to carburettor vacuum port
    Also what is the diameter of this line
    Cheers,
    Mike
     
  10. Barry
    Joined: Mar 2002
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    Barry Senior Member

    If you hook it to the vacuum line, will not the diaphragm pulse the vacuum, or is the fuel pump, dry side of the diaphragm vented to the crank case. If not vented to the crank case, would the pulse of the diaphragm interfere with a
    vacuum advance

    Every one of the marine engines that we bought from engine upfitters, had the overflow line attached just under the flame arrestor on the arrestor itself
     
  11. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Barry, you're right! As soon as I read your post I remembered where this safety line from the fuel pump attaches to my carburetor. It's not drawing vacuum, it is up on top of the carburetor under the flame arrester exactly as you said.

    I'm not sure if putting vacuum on that line would make any difference as far as fuel pump performance is concerned. My intuition tells me it wouldn't matter but I'd have to check it and see. Regardless, you're right that the line is attached on top of the carburetor so there isn't any vacuum on it.

    Mikealston, I'll post a link to the carburetor that I use. It's a Holley marine carburetor so it's a bit different than a Q-jet. Look at the picture. Look at the top of the carburetor, where the flame arrester fits on. Look at the flange and next to the secondary bores on top of the silver fuel line that connects the primary and secondary float bowls you'll see it. There is a small port there with a black rubber boot on it. That's what Barry is talking about. So it's not really pulling vacuum but in the event of a fuel pump failure it will allow fuel to flow from the pump to the carb as a safety measure.

    Holley 0-80364 450 CFM Marine Carburetor https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80364

    Thanks for straightening me out on that Barry. My mistake.

    Regards,

    MIA
     
  12. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Hi Barry And Missinginaction,

    Thank you both for clearing that up for me
    My flame arrester has the fitting on it above the secondary bores
    So the fuel pump overflow fuel will drain into the secondaries

    So I understand this would flood and stall the engine which in turn would let me know the first pump diaphragm has perforated

    If I then ran the line from the fuel pump straight into a jerry can (which I always have onboard) I could then get the boat back to the boat ramp with the last pump diaphragm ? ?

    Thank You Again Team,
    Mike
     
  13. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The small hose from the pump to the carburetor is clear vinyl to let you see if any fuel is leaking. It doesn't need hose clamps, zip ties work fine.
     
  14. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    No problem, my apologies for forgetting where that line goes in the first place. I've never had a fuel pump fail, so I don't know exactly what would happen. In the automotive world we don't use mechanical pumps anymore since everything is fuel injected. In the old days a failed pump diaphragm would cause the pump to leak and you'd see/smell gas under the car. My understanding is that while a diaphragm can fail and flood out your engine, it is more likely to fail slowly. This is why the tubing running from the pump to the carburetor is clear. When you're checking oil/doing a pre-trip inspection just take a look at the line. If you see any liquid in it that's a red flag.
     

  15. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Hi Guys,
    Ive ordered some Tygon hose for pump to carb
    Ill let you know if Ive solved the problem once I've put the boat in the water
    Thanks,
    Mike
     
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