My Merc 1150 had too lean a mixture when I had the problem. It now runs fine, I just adjusted it richer. I doubt the tank test will let you know if you have a cure. Well, it ran somewhat better in the water today, but still bogged down at times. I decided to pull apart the fuel pump, and found the gasket had one spot with some pretty severe tearing, and the diaphragm had some nice tears, too.
Fuel pumps cause a lot of bogging at w.o.t. happy boating.
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