In-Line Fuel Filter Question

christopher425

christopher425

Seaman
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Jun 21, 2022
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Hey All, I'm working on an '87 Mariner 45hp (4 cyl) and have a question re: my in-line fuel filter. I've got an OEM filter and I typically remove my fuel line after use via quick disconnect from my tanks (just for safety purposes). Is it normal for the fuel filter to lose all the fuel in it within a day of just sitting? It will hold full for about a day, then I'll go back to check and it will be bone dry. My fuel filter is oriented horizontally and it is above my fuel filter and just about even with my top carb. I know the filter itself and the hoses are not leaking and I cannot locate any fuel around the fuel pump. I just rebuilt the carbs and set everything to spec with the float/needle, etc.

My issue is that I replaced a carb at the end of last summer due to a eaten up valve seat. Boat ran the best it ever has right before storage. I ran the engine until it stalled to remove as much fuel in carbs as possible for winter storage. I get it out this year and it won't even idle. Having the hardest time and it just doesn't make sense. Fuel is good and clean. Connections are solid. Nothing has changed really. Plugs are wet and firing. After work I'm going to test the fuel pump for any leaks. Aside from the fuel pump and carbs, I'm kind of scratching my head. I really don't believe it's an ignition problem. Went through all of that last year and everything checked out. Any advice would help. Thanks!
 
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Chris1956

Supreme Mariner
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Mar 25, 2004
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The gasoline in the carbs will evaporate when in storage. If the filter is above the carb fuel level, it can drain into the carb, as the gasoline evaporates. So when you ran the 4 carbs dry, some of them still had some fuel, plus any that was still in the filter, lines etc, that could drain into them.

So your carbs sat with some fuel in them over the winter? That fuel can turn into varnish and sludge, and I suspect that is what is causing your issue. Pull the drain plugs on the carbs and pump some fresh fuel thru the. I doubt it will cure the issue, but it is worth doing. When that doesn't work, you will need to remove and clean the carbs.
 
christopher425

christopher425

Seaman
Joined
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Messages
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Chris1956 said:
The gasoline in the carbs will evaporate when in storage. If the filter is above the carb fuel level, it can drain into the carb, as the gasoline evaporates. So when you ran the 4 carbs dry, some of them still had some fuel, plus any that was still in the filter, lines etc, that could drain into them.

So your carbs sat with some fuel in them over the winter? That fuel can turn into varnish and sludge, and I suspect that is what is causing your issue. Pull the drain plugs on the carbs and pump some fresh fuel thru the. I doubt it will cure the issue, but it is worth doing. When that doesn't work, you will need to remove and clean the carbs.
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Thanks for the reply Chris. That makes sense. This motor has 2 carbs and I currently have them off and am giving them a thorough cleaning. We did take it out on the water last weekend and it would run as long as I stayed above 1000rpm in gear so that it wouldn't stall. Ran good at WOT, but died on me several times while trying to trailer it. Not a fun feeling.
 
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airshot

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Jul 22, 2008
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In my much younger days, my old motor had carb issues after sitting all winter. I made a little hand pump with a hose that would go into the carb drain plug hole. I would pump some gum out ( old time carb cleaner) into the bowl and flush out any left over crud. Worked well but very messy. Today, it is much easier to use fuel stabilizer to treat the fuel, so crud doesn't form. Even using E fuels, I have not had a crud issue in any carb in ??? actually can't remember the last time I had a carb problem.
 
christopher425

christopher425

Seaman
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Messages
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Update: Cleaned top carb really good. Wasn't that bad to begin with. Then, pulled bottom carb off and found this in the bowl. What the heck is this stuff? Could it be fogging oil that I used about a month ago and it just never got completely flushed from the bowl?IMG_0571.jpeg
 
christopher425

christopher425

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You think I've got some water intrusion? I run off a 6gal portable tank and gas is about a month old, but I've only used it once in that time and it sat for several weeks before doing so. I only use ethanol free fuel. It's been super humid here, too, all month. I wonder if that's it...
 
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cyclops222

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Mar 21, 2024
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Poor low or no idle ? Good WOT ? Water in the fuel bowl of the carbs. I just went thru the same problem. Too much water in the gasoline. I had marina empty both tanks and dry out the tanks. New fuel. Instant great running engine again.
 
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airshot

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Today, it is easy to get bad fuel from the gas station. Many stations don't follow proper handling and filter replacements like they should. Folks want to jump on E fuels to blame all their problems, but in reality, Myself and my neighbor ( old car collector) have had far more issues with non E fuels than we have with E10.
 
christopher425

christopher425

Seaman
Joined
Jun 21, 2022
Messages
62
Thanks for the help y'all. I'm gonna dump the fuel from my tank, flush the lines, install everything and run clean fuel through it. I will report back my findings.
 
christopher425

christopher425

Seaman
Joined
Jun 21, 2022
Messages
62
airshot said:
In my much younger days, my old motor had carb issues after sitting all winter. I made a little hand pump with a hose that would go into the carb drain plug hole. I would pump some gum out ( old time carb cleaner) into the bowl and flush out any left over crud. Worked well but very messy. Today, it is much easier to use fuel stabilizer to treat the fuel, so crud doesn't form. Even using E fuels, I have not had a crud issue in any carb in ??? actually can't remember the last time I had a carb problem.
Click to expand...
What fuel stabilizer would you recommend Airshot? I've used Sta-bil in the past...
 
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That old Mercury

Petty Officer 2nd Class
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Oct 12, 2023
Messages
143
I would put a fuel filter water seperator inline on it and mount it around the same height as fuel tank if possible. Roughly $30 .
And a fuel stabilizer always.
Nothing worse then getting towed back !

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christopher425

christopher425

Seaman
Joined
Jun 21, 2022
Messages
62
That old Mercury said:
I would put a fuel filter water seperator inline on it and mount it around the same height as fuel tank if possible. Roughly $30 .
And a fuel stabilizer always.
Nothing worse then getting towed back !

​

Click to expand...
Thanks for the suggestions. I've been looking into separators already. Appreciate it!
 
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Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
27,817
High volume gasoline stations have the least water in their tanks. They have thought of raining when filling. Stick with them for clean fresh fuel.

Do install a water separator, however.
 
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