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  • Fuel spilling from vent

    I have a 1972 Mako 19ft. I recently redid the coffin lid. Sealed everything up and now when fueling tank for the first time it spills as if tank is full. Fuel also comes out of vent. I thought maybe vent was clogged but then why would gas be able to flow out. I tried pumping gas slowly but still not flowing. So does anyone have any suggestions.
    1972 Mako 19

  • #2
    Silly question but are the hoses connected correctly? not sure how it is traveling up the vent hose if tank is empty. Was there any rain when the lid was off that maybe got water in the tank?
    [br]1984 Mako 224[br]1977 Mako 15[br]Clermont, Florida- [br]http://www.classicmako.com/forum/topic.asp?TOPIC_ID=37212 -Rewire[br]http://www.classicmako.com/forum/topic.asp?TOPIC_ID=40627 -Tank/Misc[br]http://www.classicmako.com/forum/topic.asp?TOPIC_ID=58615 - Aft Box removal

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    • #3
      Hi - I would check that vent line again for a restriction. Just before it exits to the vent there is usually a loop of some kind to keep water out of the vent tube to prevent it running down into the tank. Over time if that vent line was pulled or for whatever reason it gets flattened near that bend you'll have a restriction. The volume of fuel rushing in is going in faster than the vent can let the air out (plus there's probably a little fuel in the vent line too) so the fuel will back up through the fill tube and overflow. You probably will still get a little air and fuel coming out the vent but again the pressure differential is pretty high and makes the fill tube back up and overflow...Hope this works...

      Best,

      Bob S
      [br]

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      • #4
        Thanks for your responses. Im not sure if water got into the tank, got me wondering now. I did redo the cofffin lid and sealed everything. I would hate to have to remove it. I snaked the vent with some wire and got at lease 4-5ft of it in with now problem. I can see gas in the fill. Also I tried to remove Fuel line where the blub is and gas came flowing out of the elbow on the tank. I figured it would release some air. So if there is some fuel in the vent, can there be air stuck in the tank making it pressurized?
        1972 Mako 19

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        • #5
          Is the tank full? You say that you redid the coffin lid. Did you also replace the fuel tank? If you know that the tank is not full, then you probably have fuel (or some other restriction) in the vent line. Try compressed air through the vent to clear it but if there is still fuel in the fill, expect that to come up and out when the air goes in...
          Toronto, Canada
          76 Mako 23
          https://forum.classicmako.com/forum/...t-s-23-rebuild

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          • #6
            Tank was in good shape. It was replaced in 2002. It appears the tank is full. Gauge says full when I turn the ignition on but while on the water it shows 1/4 full. Im going to try and siphon our whats in the gas tank.
            1972 Mako 19

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            • #7
              Hi Allen - before you drain the tank. the sending unit for the fuel gauge is hooked up to some sort of mechanical float device in the tank itself..They are far from perfect. It's possible that mechanism could have gotten stuck down a little which is why you had the difference in readings in the water or out.. It does sound to me like the tank is full and the vent line is full of fuel or restricted in some way. What would cause the tank to be full of water anyway if you think about it? Can you take a sample of the gas from the fuel line before it goes into the water sep filter? If there is water in the fuel it will separate and you'll be able to see it..

              Bob S
              [br]

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              • #8
                Thanks Bob I am going to try that and let you know what happens. I also dumped a bottle of sea foam in there.
                1972 Mako 19

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                • #9
                  Thanks Bob Im going to try that and let you know what happens. I also dumped a whole bottle of seafoam in the tank.
                  1972 Mako 19

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                  • #10
                    Just an additional note in response to your comment about the tank being pressurized..I am up here in CT..I stored my boat one winter with a full tank. Every time the temperature got up to about 50 degrees fuel started dripping from the vent. The gas was expanding in the tank.I've since found out the boatyard I'm in recommends not storing with more than 3/4 of a tank for just that reason...just a little more to think about LOL
                    [br]

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                    • #11



                      1972 Mako 19

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                      • #12

                        1972 Mako 19

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                        • #13
                          Today I removed water separator filter and dumped it into a bucket. Gas was brown and I can tell water was in it bc it started to separate. So I went a bought a siphon and removed 30 gallons of gas. Some looked to be ok but once I got to the bottom of tank it was pretty bad. Tomorrow Im buying a 6 gallon external tank to run clean fuel and clean out the carbs in the motor. I have a good feeling about this we will see what happens. I was also told to dump a couple of can of dry gas in tank. Them fill with gas and can of sea foam. Does that sound right ?
                          1972 Mako 19

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                          • #14
                            The vent hose must have a loop that it higher than the vent opening. The vent line should not have any points lower than the connection to the tank. These two requirements insure that there is no spot in the vent line where fuel or water can pool. It either drains out of the vent or drains back into the tank. If fluid pools in the vent line, it will created a back pressure that causes the tank to not fill correctly.

                            The gas tank fill line also should not have low spots that pool gas.

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                            • #15
                              It turns out to be tank full of bad fuel and a bad sending unit. I siphoned our 30 gallons of water and bad fuel. The last 2 gallons to siphoned by sticking tubing directly into hole where I removed the sending unit and got the last drop. I also took rags tapes to a hanger and cleaned up as much as I could. Last I through in some stabil in gas tank to clean up some residue. Now time to fill and test .
                              1972 Mako 19

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