A few weeks ago, one of my engines wouldnt go over 3500 RPM,started to breakup and start stalling, other engine OK. Today I changed the spark plugs. One engine still start no problem, the other turns but doesnt start.
I had the same issue. Engines ran fine in the water, went home to flush them out and the port wouldn't start. Tried a few days later, no start. Couple days later, swapped the plugs and it fired right up. I have no idea what the deal is, but I imagine your issue is probably in the carbs. Seems like they're the root of all evil on our boats...
