Revert back to post #9 or get a friend (or someone qualified) that understands basic marine / automotive wiring to help.
Mistakes can be costly by allowing the magic smoke to escape and turning you project into a cinder.
Only downside of the tube is that if your engine doesn't run correctly (rich / lean or burn some oil), the tube will allow a film yo form on drive unit and the rear of the boat and a very slight increase of sound. Whereas the bellows directs it all thru the prop. The 4 cyl probably will sound a...
If you place it in forward gear (engine not running), the prop will free wheel, with clutch dog clicking loudly, when turned in clockwise direction.
Don't know if I explained it to you clearly enough, but from what I think you are saying, sounds like yours is working correctly.
Have you checked your fuel pressure at different speeds? Sounds like pump isn't keeping up.
Or, the fuel system supply has a problem, like a fuel line deteriorating internally, plugged tank vent, dirty fuel intake strainer or bad anti siphon valve.
