I have a Mariner 45 on my pontoon boat. In trying to use it this year, found that the top carburetor was clogged. Took it to repair shop, he use a 'quick clean' solution to try to break it free. It didn't then so I was told to take it to lake, engine in water, and run til it broke free. Ran it a high rpms for about 20-30 min. It finally blew black stuff out, then needed carb adjusted. Took it again to lake, still kind of sticky. Another person got in under the carb and more black stuff. But then he said it didn't sound good that because it was run without 1 carb working (the other one was fine) that the cylinders didn't get enough oil and that if I were to use it, the motor would seize. Don't know who to believe.
