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1988 115 hp Mariner 2+2 Rough Idle

J

JDraz

New member
Have a 1988 Mariner 115HP 2+2 and decided to change the plugs as at idle it was running rough. The result was a rougher idle and stalling. Great at anything above a low idle. Have checked the gaps and wires. Have heard about plugs having to be lined up but havent tried anything.
Any ideas would be appreciated.
 
Re: 88 115 Mariner 2+2 Rough Idle

Got spark to your number 1 and 2 plug?

Old gas?

Water in gas?

More history is needed here.

When was it last running ok? Has it just come out of storage etc...
 
Re: 88 115 Mariner 2+2 Rough Idle

Thanks for your assistance.
Have run the boat about 10 times this year through about 3 fillups of my 2 plastic tanks. Ran great so far.
Issue started on last trip when it ran rough at trolling speed and idle. Great at mid to high speed, purrs along.
Sputters and stalls at low speed.
Would not think it was water in tank but it's an easy thing to check.
As for the spark, it's performance at mid to high speed would seem to indicate that it is getting a spark. Changed the plugs as it was easy enough to do. As mentioned bottom plug is brown and normal looking, get wetter and darker up to top plug.
Thanks,
 
Re: 88 115 Mariner 2+2 Rough Idle

If the top plugs are a little wet looking the fuel is probably getting through ok. And I would expect #1 and 2 to be a little darker since these are you (idle) cylinders in the 2+2 format.

So, barring "bad gas" I would next troubleshoot the coils - you may simply have a weak one (on the way out) in one of your top two cylinders.

You could try swapping your 1/2 coils with 3/4 - that's the "cheapie way" to test them. Then if you idle and just off idle smoothes out you know one of the coils is bad.

That would be my next step if I was working on this motor myself...
 
Re: 88 115 Mariner 2+2 Rough Idle

Thanks for the suggestion, I took it out for a ride a couple of nights ago with new fuel (son caught a nice chinook) so it was worth the trip but I did notice one thing.
When cold it idles fine. Warms up and idles out of the harbour nicely. Runs great out to the fishing spot where I run my kicker to troll.

Runs great on the way back in until I throttle down in the harbour when the sputtering begins.

Not sure if this adds adds any clues but I will try the coil suggestion.

Thanks again for your reply. This is the first time I've posted and I am very appreciative for the suggestions. Not shy with the wrenches or learning, just have little knowledge of the operation of an outboard motor.
Regards,
JDrazic, Nanoose Bay, B.C.
 
Re: 88 115 Mariner 2+2 Rough Idle

That actually points to a fuel problem and not ignition at all.

It's possible that what you are experiencing is one or more of the carbs is starting to flood.

The usual suspect is a sticky float valve and if first shows up when you "throttle down" after running. It doesn't quite close properly allowing a excess of fuel into the carb which "bogs" things down.

At a very early stage, such as yours, often an additive to the gas can correct it.

SeaFoam is hard to find up our way, but try one of the gas additives from (crappy tire) for small engines - any of the "add to gas" carb cleaners or "tune up" in a can.

At the very least, the products are only a couple bucks and won't hurt anything even if the problem turns out to be something else, or, ultimately requires a new float valve...

(and a minor flood would really explain the wet plugs)
 
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