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Running back from the beach last weekend, at WOT, 5500 RPMS, about 34 MPH, when suddenly the motor lost 1000 RPM's and 10 MPH. Stopped to listen and the motor just didn't sound "Right". Not the usual OMC 2 cycle, three cylinder sound I am used to. Much quieter as if missing on a cylinder. Was able to motor the last few hundred yards back to the dock and started looking into the problem... changed inline fuel filter on motor, re-filled 6 gallon plastic portable tank with fresh premium fuel, checked compression (125 LBs on all three cylinders), have spark on all three cylinders. Drained carb bowls, sprayed with carb cleaner, still doesn't sound right and can't get more than 4500 RPM's. And after draining and initially restarting by spraying some carb cleaner while cranking the motor, haven't successfully restarted the motor. Mechanic tells me he thinks one or more of the jets may have become clogged and carbs need to be torn down and rebuilt.

I am tempted to believe him with all the ethanol horror stories we hear, but I am wondering about one more thing... I had to change a two year old battery immediately before this because it didn't appear to be holding its' charge. SO I am wondering if the battery was really okay but if something's wrong in the stator / rotor / rectifier/ignition system? Mechanic says "You either have Spark or No Spark" but I am wondering if anything here sounds familiar to anyone... thanks for your thoughts if any...

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Brooks,

I had a simliar problem with my Yahama 40hp. The solution was to take the carbs off, remove the bowls and literally spray carb cleaner into the jets themselves. I think your mechanic may be correct in telling you the jets might be clogged....that was the case with my motor.

Hope this helps.

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Brooks,
When you pulled the plugs to check compression were they all the same color? Was one of them wet? Does that engine have a separate coil for each cylinder? The color of the plugs can tell you a lot.
Mike

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Brown and dry, 3 coils, 3 carbs.

My initial guess was a bad coil, (I was actually hoping that was the problem as it's the easiest, least expensive problem to solve!) but mechanic at the parts counter was guessing a bad power pack and recommended a compression test before anything else. The result was good even compression numbers. And spark on all three cylinders. That's what led him to recomend doing the carbs.

But I don't generally believe in coincidence and that's why the battery charging thing bothers me. I don't have the tools and knowledge to do the diagnostics on the electrical system... how would one test the rectifier? How do you test a coil to see what voltage it's putting out?

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Brooks, I initially thought my problem was the coils too. I took a known good coil from a good cylinder and swapped it with suspected bad cylinder and the gripe did not follow. So I went with the carbs based on the advice of a 35 year experienced Yamaha technician. Come to find out, he was right on the money. If your mechanic tells you he suspects the carbs, I bet he's right.

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I guess 8 years virtually trouble free is a pretty good run. And better now at the tail end of the season than the middle of the summer. Still aggravating anyway.

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Mystery solved...sort of. The problem turned out to be a 1" long 5/16" stainless bolt lodged in the reed valve behind the bottom carb! Friend's father, a semi-retired, part-time outboard mechanic discovered it in there... Now the question is where did it come from? It's identical to the bolts that OMC used to fasten the air silencer to the carbs. I'm going to look further at OMC's parts diagrams and see if it's the same part number...I have half an idea the bolt's probably been bouncing around in there for eight years waiting to get stuck in the valve.