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Old 26-03-2016, 11:29   #1
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Question Yamaha Outboard 2-stroke 15-hp Misfiring

My outboard motor runs but misfires every few seconds. The motor is 15 2-cylinder, 15-horsepower 2-stroke, about eleven years old. The model number is 15MSHD. The engine runs like "brrrr puff brrrr puff brrrr puff." It makes a puff of smoke in the exhaust with each misfire. It powers-up with the throttle control, the forward and reverse work fine, and the water pump output is strong. I have dismantled and cleaned the carburetor, poking wires through all the orifices, replaced spark plugs one-at-a-time, and replaced ignition coils one-at-a time. I only purchased one new spark plug and one new ignition coil, as it seemed likely that only one component is bad. I would appreciate any suggestions to isolate the problem. Thanks, Porter Howard s/v Cinnamon Teal, Currently in Panama

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Old 31-03-2016, 19:23   #2
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Re: Yamaha Outboard 2-stroke 15-hp Misfiring

Cleaned the carburetor a third time at suggestion of marina mate, using carburetor cleaner and fine wires in holes. I think I got a couple holes I missed before. Motor runs steady now; no misfiring.

Porter Howard, s/v Cinnamon Teal, currently in Panama. Jesus is Lord and Savior
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Old 01-04-2016, 03:30   #3
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Re: Yamaha Outboard 2-stroke 15-hp Misfiring

I have a 5 hp Yamaha 2 stroke that would not idle. Took the carb off three times and cleaned. Still problems. A mechanic suggested that maybe it was due to the slow idle chamber being clogged. Never heard of that though. On a 5 hp Yamaha, there is a plate on the top of the carburetor, under the swivel for the throttle that has two screws. I unscrewed this and lifted the plate. Sure enough there is a couple of chambers that the gas goes through when the engine is at idle. I cleaned the area out with carburetor cleaner and the engine now runs great again. Easy fix.

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Old 01-04-2016, 04:41   #4
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Re: Yamaha Outboard 2-stroke 15-hp Misfiring

Greetings and welcome aboard the CF, Porter.

Good on yah, and thanks for the update.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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