1997 Evinrude 115 misfiring

1. The air temp was 40 degrees as apposed to 60 and higher.
2. I had a pretty good dose of STA-BIL fuel stabiliser in the fuel tank.

Still Afloat said:

So the 97’ Evinrude 115 2 stroke on my Crestliner has been giving me fits. It starts missing real bad at about 1/4 to 1/3 throttle. This all happened, possibly coincidental, after the boat was partially swamped in a storm.

I first thought that it had water in the fuel so I completely drained the tank, replaced the water separator, replaced the fuel line/priming bulb from the separator to the outboard and replaced the fuel filter on the outboard. They were probably all due for maintenance anyway so nothing lost.

The problem persisted and I turned towards the ignition system. The spark plugs did’t have many hours on them but, I tried a different set with no change. The potting on the ignition coils was cracked quite bad so I replaced them. Figured if they weren’t failing already they probably would fail soon. At this point the problem went away so I hung some for-sale signs on it. Took it out to lake for some fishing (and advertisement) and it started missing again. Took off the signs and took it back out again with a timing light to see if I could detect a miss on one cylinder. Visually, they all seemed to be firing fine but, it was still missing with a bit of throttle. I ordered a couple of carb kits with the intent of rebuilding them this winter.

I have not gone through the carbs yet. The boat was run all season on electric, only using the OB at low speeds mostly to launch and load.

So after fishing last Sunday I fired it up to idle back to dock and it sounded a bit smoother so I accelerated and it ran fine. Did a couple laps around one end of the lake and no problem. Maybe the max rpm’s were down 400 or so but, I was cold at this point and headed in.

There are really only two things I can think of that changed since it last ran Ok.

1. The air temp was 40 degrees as apposed to 60 and higher.
2. I had a pretty good dose of STA-BIL fuel stabiliser in the fuel tank.

Could the Stabil have removed some gunk in the carbs? I’m not convinced that the problem is solved. At least until I take it out a few times and that may or may not happen this season.

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Sea Antsy said:

? Did you replace the spark plug wires as well as the coils.
I would try disconnecting/cleaning every connector,lug,ground, first..
next try to put a dc volt meter on the output of your voltage regulator and watch the voltage as you rev up UNDER A LOAD.

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Stand Up said:

I don't know much about 2 strokes but I would look for fuel blockage as it sounds like the motor isn't getting all the fuel it needs all the time.
Clean out the fuel tank and be sure it is clean. Little bits of crud in there will cause problems intermittently as you have described. It sounds like you have already done this.
Look for cracked or leaky fuel lines as well. Fuel lines should be like new.
Fuel that has too much ethanol may give you trouble as well. And the symptoms are quite like what you described.
I'll be interested in what the trouble actually is to learn more about the 2 stroke engine.

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David Atkins said:

Simple but can be complicated, as the two-stroke’s piston rises on compression, its underside pulls a partial vacuum in the crankcase. An intake port of some kind (cylinder wall port, reed valve or rotary disc valve) opens, allowing air to rush into the crankcase through a carburetor.

When a 2 stroke sits the fuel can become contaminated thus all of the fuel system entry points can be clogged or loaded up with junk. Could have been the reed valves, cylinder wall port or disc valves sticking, not sure which one you have but I suspect that was issue since you said it ran fine later!

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thill said:

Did you ever drain the bowls of the carbs? A little water sitting in the bottom of a bowl can cause some big headaches.

I would look at the carbs and fuel system carefully, as fuel starvation in one carb can destroy the engine. Spark issues generally won't hurt the engine, it just won't run well.

Pull the carbs and clean them out carefully and put in new gaskets, not screwing the bowls on too tightly, as that warps them. You might want to add a healthy dose of SeaFoam. You can't add too much. 2 oz./gallon is a good treatment dose, and will sometimes clear up some problems. But you need to run the boat several times after treating so that it will work.

I hope you get it figured out.

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Still Afloat said:

The tank was cleaned out down to the last ounce or two through the fuel gauge port. I have not replaced the fuel line between the fuel pick-up and water separator. It does not have cracks or leaks, seems pliable. It’s not the cheap grey stuff.

I could not see the pick-up tube when servicing the tank. If it has a screen perhaps there is some blockage. I will replace that section of fuel line just to eliminate it and blow some air back through the screen before buttoning things up.

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Sea Antsy said:

...blowing air thru the pickup tube might not be the best process... I have seen jelly like "tar baby balls" get coated all over that fine screen.. mostly in sailboat diesel applications, but.. since you got a watersep/fuel filter installed might be brave to coat hanger thru that screen...

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