Boat won't crank! G3 Talon, 90hp yamaha 2 stroke

[ahlangle]

My cousin's boat has been in garage for about 6 months. It's a G3 Talon 17' with 90hp Yamaha two-stroke (probably about a 2005 model).
He says battery is charged and when he turns key, it's firing but not cranking all the way up, almost like it's not getting enough fuel.

Battery is 100%, put new spark plug in, and has gas.
I think the fuel is bad (6 months+ and never uses additives) or he has water/crud in it.
Possibly kink in fuel line, but I believe it's got something to do with the fuel or fuel delivery system.

Can anyone shed some light on this?

Thank very much.