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M Engine Fuel Bowl Gasket

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tparsons56
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M Engine Fuel Bowl Gasket

Post by tparsons56 » Mon Jun 10, 2019 8:47 am

This spring while fitting out I noticed a small amount of sediment in the bottom of the glass bowl so I took it off and cleaned it. While putting it back together I filled the bowl with fresh gas as high as I could go without it overflowing and then pumped the fuel pump to pressure. I noticed the cork gasket didn't look that great but after installing nothing leaked while running the engine but there were some air bubbles at the top of the glass bowl.

Yesterday we went for a cruise and the engine ran great until we idled back. The engine couched a couple of times and then died. We could not get the engine started again and got towed back home. On quick inspection the glass bowl appeared full of gas but with the same air bubbles.

I'm thinking the gasket is letting in air under suction - does anyone know if there is a precut gasket for these bowls or does anyone have an other ideas of what might be the issue? Is air bubbles at the top of the bowl normal?

The gas tank is about 5/8 full of last years gas but I did stabilize it last fall.

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Bilge Rat
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Re: M Engine Fuel Bowl Gasket

Post by Bilge Rat » Mon Jun 10, 2019 1:53 pm

Replacement fuel bowl gaskets for the AC pumps are available in cork and rubber. I have always used the cork ones as I had a rubber one shrink once when I removed the bowl for cleaning, Possibly from an ethanol fuel issue incompatibility. If the gasket is leaking, the bowl is on the suction side of the pump and you could very well be sucking air and not creating enough vacuum to deliver fuel to the carb all the way from the tank. I no longer use ethanol enhanced fuel as where I live, high octane ethanol free gas is available. I also drain the fuel tank for the off season storage and make sure to run the carb dry when prepping the engine for the winter.

If you manually operate the priming lever on the pump to fill the carb float bowl does it start or does the pump bowl never fully fill? If it doesn't fill, a suction side leak is quite possible. If you give the carb a shot of ether (not too much!) does it cough like it wants to start? That would indicate a fuel delivery issue. It could be something other than a fuel issue causing the no start condition.

Year old gas, particularly if it has the ethanol additive can absorb a lot of moisture in that time, even if a stabilizer was used. Since water sits on the bottom of the tank, you can use a product like Gasoila All Purpose Water Finding Paste on the end of a stick to probe the bottom of the tank and note the color of the paste. That way, you will see if water in the gas is the problem.
Last edited by Bilge Rat on Mon Jun 10, 2019 2:22 pm, edited 1 time in total.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

tparsons56
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Joined: Tue Jan 25, 2011 8:02 am

Re: M Engine Fuel Bowl Gasket

Post by tparsons56 » Mon Jun 10, 2019 2:04 pm

The boat started and ran well at the beginning of the season and the first couple of times that we ran it but they were only short distances. Yesterday was the first time we ran it for a longer distance so maybe it allowed more air to get in. When I manually would prime the pump I would see air bubbles swirling around the top. I am ordering a new gasket so hopefully this will resolve the issue.

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Bilge Rat
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Re: M Engine Fuel Bowl Gasket

Post by Bilge Rat » Mon Jun 10, 2019 2:15 pm

The Zenith carb on an M engine should have a drain plug on the bottom of the float bowl. It is not the plug that is at the bottom of the air horn bend towards the front bottom of the carb. If lack of fuel delivery is the issue, removing the bowl plug and seeing no gas pour out might confirm no gas is being delivered.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

tparsons56
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Joined: Tue Jan 25, 2011 8:02 am

Re: M Engine Fuel Bowl Gasket

Post by tparsons56 » Mon Jun 10, 2019 2:27 pm

I will check that. Thanks for the input!

jim g
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Re: M Engine Fuel Bowl Gasket

Post by jim g » Wed Jun 12, 2019 7:56 pm

If the fuel bowl gasket is over a year old. They usually won't reseal after the bowl has been removed. The cork ones get hard. Rubber ones leak. I think its the additives they put in todays fuel. Which are the same whether it has ethanol in it or is ethanol free.

You can get a sheet of cork gasket material from napa and make your own gasket. Take your old one so they can get you the right thickness.

John Justice
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Re: M Engine Fuel Bowl Gasket

Post by John Justice » Wed Jun 12, 2019 8:26 pm

tightening the bail nut on the fuel bowl too much can distort the sealing surface of the fuel pump, making it difficult for even a new gasket to seal.

tparsons56
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Re: M Engine Fuel Bowl Gasket

Post by tparsons56 » Thu Jun 13, 2019 8:15 am

I have a new gasket coming from Finewoodboats which I will install this weekend which hopefully solves the issue. In the past on other boats I have put a thin film of waterproof grease on both side of the gasket to hold it in place during installation. Any issues with this?

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Bilge Rat
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Re: M Engine Fuel Bowl Gasket

Post by Bilge Rat » Thu Jun 13, 2019 8:47 am

Jim Dandy at Finewood Boats to the rescue again. I don't think a little waterproof grease should be an issue, but there is a fine mesh screen at the top of the bowl that you wouldn't want to get plugged up. As an aside, do you have a modern fuel filter upstream of this? Changing the cartridge on that is a lot easier than removing the glass bowl in a tight engine compartment as a lot of that work is by feel not vision. Just be sure to use a marine rated filter, not an automotive style and flare fittings on the copper lines.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

tparsons56
Posts: 44
Joined: Tue Jan 25, 2011 8:02 am

Re: M Engine Fuel Bowl Gasket

Post by tparsons56 » Thu Jun 13, 2019 1:34 pm

I just received the new gasket and it is much thicker and better made then the existing so hopefully this does the trick. I do not have an aftermarket fuel filter but the tank and all the lines are new as of 2016. If I take the back seat out it's not too bad getting access to the bowl - the big trick is not letting the bolt that holds the bowl from dropping into the bilge. I just need to make sure I have a foil pie pan underneath.

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