Yamaha Outboard 2-stroke 15-hp Misfiring

[PorterHoward]

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

[PorterHoward]

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.

[landonshaw]

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.


Sent from my iPad using Cruisers Sailing Forum

[GordMay]

Greetings and welcome aboard the CF, Porter.

Good on yah, and thanks for the update.