Pontoon Boat & Deck Boat Forum

my 1997 70 horse Yamaha bogged down on the way back to the ramp. When I got home I pulled the cowl and when I pulled the spark plug on that cylinder it looked like unburnt fuel was leaking out of the top cylinder and the cylinder was not firing. I changed the spark plug out to make sure I had a good plug in it. Still not firing. Any thoughts would be appreciated.

Before you go any further do a compression test on all cylinders... You will know something is wrong right away. I had 3 at 120# one at 90# when mine failed.

From there, you'd need to clean the carbs looking for sticking needle valves.

90/10 gasoline is tough on fuel systems, including gumming up the carbs. Fortunately, cleaning carbs is a 15 minute job after they're on the bench.

bassandtoon wrote:my 1997 70 horse Yamaha bogged down on the way back to the ramp. When I got home I pulled the cowl and when I pulled the spark plug on that cylinder it looked like unburnt fuel was leaking out of the top cylinder and the cylinder was not firing. I changed the spark plug out to make sure I had a good plug in it. Still not firing. Any thoughts would be appreciated.

In bogged down I'm assuming it's running but missing on the fowled cylinder. The first thing I'd do is to take a known good plug and find a good ground on the engine. Put the wire boot on the good plug hold it against the ground and have someone turn the engine over observing for "Spark". If no spark is seen look upstream to the coil pack(s) for the problem. If spark is observed follow the progression as others have already suggested..