no, just run it first: I think you are over complicating things. Unless you cool the engine with liquid nitrogen it will not stall.
But elaborate a bit on what you have set your needles at, what carb you use and may be some pictures. You're making this a complicated puzzle, that I think just originated from the butterfly at the carb being closed completely and no coil or other needle issue. . If you have a WT257 carby: L needle 2,25 turns out ( from closed) and H needle 1,25 turn out, your butterfly not complete closed, it should run.. And yes it's a boat so tune it under load on the water, not on land with no load.
But elaborate a bit on what you have set your needles at, what carb you use and may be some pictures. You're making this a complicated puzzle, that I think just originated from the butterfly at the carb being closed completely and no coil or other needle issue. . If you have a WT257 carby: L needle 2,25 turns out ( from closed) and H needle 1,25 turn out, your butterfly not complete closed, it should run.. And yes it's a boat so tune it under load on the water, not on land with no load.