1986 Mariner 115hp Engine

[brianwag]

Last Saturday I went out in the boat and noticed that I had to pump the fuel bulp a few extra times before I could get it started. So when I returned home, I replace the in-line fuel filter with one that has the glass viewing window with a replacable filter. I also added a fuel cleaner on the same day. On Sunday, I could not get the engine to idle at all. It would crank but die right away. I had to give it gas in order to keep it idling. I went out thinking that it would eventually clear itself out. However, the entire time I would have to crank it while giving it gas and throw it into gear with half throttle to keep it from dying. So logically to me it has to be either the fuel additive or the filter. One thing I noticed was the filter never stays full of fuel. However, when it starts to die the filter begins to fill up. My thoughts was that maybe the filter is allowing air to be sucked in causing an issue with the fuel flow? The engine runs fine at full throttle and doesnt miss a beat? (Oh and I made sure the filter was correctly installed with the in and out flow.) I was also wondering if I needed to put teflon on the nylon fittings for the fuel filter? Looking for ideas thanks for the help...

Brian

[jerryjerry05]

Sounds like there is water in the system or the pump needs rebuilt.
Do a compression test too.J

[Texasmark]

Corrolary: I had a Chev with a Quadrajet Carb. Had this tiny filter in the fuel inlet of the carb. I thought I'd put a regular sized inline filter in the flexible inlet to the fuel pump...since the outlet line of the pump (to the carb) was steel and difficult to tap into as compared to the rubber line.

In short, adding the "resistance" of the filter in the line caused the fuel pump to "suck against" the resistance, lowering the atmospheric pressure of the fuel and causing it to boil, hence "vapor lock" and the engine would quit running.

Might be some correlation here that may help you.

Mark

[fisherman81654]

Last Saturday I went out in the boat and noticed that I had to pump the fuel bulp a few extra times before I could get it started. So when I returned home, I replace the in-line fuel filter with one that has the glass viewing window with a replacable filter. I also added a fuel cleaner on the same day. On Sunday, I could not get the engine to idle at all. It would crank but die right away. I had to give it gas in order to keep it idling. I went out thinking that it would eventually clear itself out. However, the entire time I would have to crank it while giving it gas and throw it into gear with half throttle to keep it from dying. So logically to me it has to be either the fuel additive or the filter. One thing I noticed was the filter never stays full of fuel. However, when it starts to die the filter begins to fill up. My thoughts was that maybe the filter is allowing air to be sucked in causing an issue with the fuel flow? The engine runs fine at full throttle and doesnt miss a beat? (Oh and I made sure the filter was correctly installed with the in and out flow.) I was also wondering if I needed to put teflon on the nylon fittings for the fuel filter? Looking for ideas thanks for the help...

Brian

Maybe the fuel pump needs rebuilt.

[CharlieB]

Small filters should be installed on the pressure side of the fuel pump, between the pump and carbs.

Larger filters such as a water separating fuel filter should be installed between the tank and the fuel pump.

The major difference is the flow ratings of each, the pressure or vacuum placed on them can affect overall flow of the system.

Failure ofo the motor at low speeds, yet seemingly running fine at high speed can often be caused by dirty carbs failing to pass enough fuel thru the idle circuits.

Before tearing the carbs off for cleaning, do a couple of simple tests.

Check fuel flow to the carbs. Disconnect the fuel line to the carbs, point it into a suitable container, pull the lanyard to kill the ignition. Crank the motor and watch the fuel stream, you should see a nice fat pulsed stream of fuel at least an inch and a half from the hose. Any less is cause to look for restriction in the system.

Temporarily replace the hose to the carbs with a clear hose and start the motor. Watch the clear hose for any air bubbles passing thru, indicating air sucking into the system before the fuel pump. Remove the clear hose once finished with repairs as it is not rated for marine use.

Once your motor has passed these tests and you still have low speed problems, order carb kits and clean your carbs.

[brianwag]

Thanks for everyones input.

I finally got around to pulling the cover today and noticed a film of gas and oil by the carbs. I didnt see any drips of fuel, but there was a small buildup by the fuel pump. Im thinking that there may be a leak from one of the hoses. The top carb was dry and clean. The bottom two had fuel and oil. Im assuming that this is not normal. However, with the carbs mounted sideways could that be normal? Under the engine compartment is also has a film of oil / fuel. Im going to try what CharlieB suggested to see if I can see any fuel leaks in the hoses.

Fuel Pump
Attachment 123095

Top Carb
Attachment 123096

Middle Carb
Attachment 123097

Bottom Carb
Attachment 123098

[brianwag]

Ran the motor today with the cover off and discovered that the top cArb is pouring fuel out of what I think is the bowl vent. It's a brass screw on top of the fuel bowl. This would explain why it runs fine wide open. Im assuming that once it fills up its not shuting off the fuel flow to that carb and flooding it. Now I guess I need to rebuild the carb. Is this easy or should I have someone else do it?

[brianwag]

Ok going to close this one out.
Symptoms: Engine will not idle. Engine runs fine when throttle is wide open.
The number one Carburetor fuel bowl float and needle valve was bad. This issue allowed the fuel to continue to flow until it flooded the Carburetor / Engine. I found a local dealer that had new parts for it and replaced the float and needle valve.
I took the boat out on a local river after replacing the parts and it ran like a champ. I think this was a problem for awhile as the motor has never ran this good since I purchased it Labor Day weekend (September).
Thanks for everyone’s input and help.