Help needed - Trouble shooting Merc. Mariner 115. I'm a shade tree car mechanic and..

Have a 115 mariner say about a 86 or 87 model. Came on a game warden boat bought from Nashville, TN govt auction about 8 years ago. Used by my friends Dad and then sat for last 5 years.

We have done the following tune up/prep items:

- replaced water imepller
- rebuilt fuel pump and check valves
- new plugs
- new wires
- new fuel line to tank and primer bulb
- replaced all 6 coils
- rewired a few corred wires that were from stator and also on harness to coils.
-

the motor runs but has a 'stall' or 'stutter' for lack of a better name. It idles fine for a minute - then next may display the stutter. You can rev it and hear it stutter. Once under load it will not get up to full rpm when on the water. Feels like a fuel problem, however, will occasionally run OK. Seems to be a combination of what I would call (if it were a car) a fule starvation or ignition issue.

We have verified fule pressure at and after pump is within spec. Carbs look clean and are all getting fuel. We rplaced the coils when one tested to be lower on spark output then others.

Any ideas?

GOD BLESS!

john

Re: Help needed - Trouble shooting Merc. Mariner 115. I'm a shade tree car mechanic a

Did replacing the coils cure the 'weak spark'?

Re-insulating stator wires is a touchy subject. 200+DVA can be hard to contain without perfect seal, any arcing/shorting and you have a 'missing spark' on one or more cyl's

Testing with a DVA meter proves good/bad, no doubt.

Download the troubleshooting manual, follow links at www.rapair.com

Re: Help needed - Trouble shooting Merc. Mariner 115. I'm a shade tree car mechanic a

Pull the fuel line out of the fuel tank and inspect the pickup screen for varnish, goo or other foreign crud. Goo would be from a moisture eliminator combining with water and making the mess. It moves about at will and if it gets sucked up on your fuel pickup screen it could cause problems as you mentioned.

While you're in there check the tank for cleanliness.

Mark

Thanks CharlieB and TexasMark.....

Thanks CharlieB and TexasMark.....

I mentioned I was a shade tree mechanic - shade tree for me means I have good basic knowledge and good basic tools. I don;t have the equipment needed to check the DVA - good idea. I have a buddy with some good diagnostic tools and this could also be a reason to go and buy some tools

I can and will pull the fuel pick up from inside tank today to check it out.

We are fortunate to have an extended season (live in middle Alabama) so I still have time to get it running and well tested this year.

I appreciate your input.

GOD BLESS!

john

Re: Help needed - Trouble shooting Merc. Mariner 115. I'm a shade tree car mechanic a

Symptoms sound a lot like a faulty electrical item. I went through a similar experience this spring. A DVA meter is a great investment for troubleshooting this scenario. Given the high cost of replacement parts, it gives comfort to be able to diagnose specific items (switchbox, stator, trigger, coil, etc.) rather than just tossing parts at it.

Do you have an inductive timing light to test for spark signal while running? They are a handy way to visually spot a misfire problem while still allowing the spark plug to function. I was able to watch the light, and see the intermittent spark easily.

Re: Help needed - Trouble shooting Merc. Mariner 115. I'm a shade tree car mechanic a

Nothing wrong about shade trees. Much cooler under there.

Try hooking up and running an electric fuel pump to see if your fuel system is taking in air from some where. I wired one into my 150 to over come a small micron fuel filter restriction. I only need to turn it on above 3,000 rpm's right now till I can get the correct pressure regulator so I don't flood the carbs. Running any engine too lean on fuel will eventually cause a piston or pistons to melt.

To check for weak ignition, double a mechanics rag and place the spark plug on the rag against the block. It takes more kva's to fire a plug under compression, this rag similuates this. If you're still getting a "blue" spark with the rag under the plug, your coils are good.

If your ignition triggers are moved by the throttle under the flywheel, unhook your throttle cable from the engine, and redo the ignition test with the spark advance in different positions. Keep your battery charged and don't over heat the starter doing all 6 cylinders too quickly.

Re: Help needed - Trouble shooting Merc. Mariner 115. I'm a shade tree car mechanic a

Spunwheels
He's verified the fuel pressure. Anything over 2 lbs, and preferably below 5.5 lbs under all conditions is fine.

hope it helps
John