without a scan and or scan tool u will need a bigger dart board to keep on throwing darts at it.

IMO best guess here would be leaking injectors and or MAP sensor

TBI injectors here and they are good at times for leaking actually with age they become very good leakers of fuel. I know I test and flow test fuel injectors daily during boating season.

OK very hard not to speak up here - I am lost you posted SCi and then mentioned CARB and then mention tps in your first post - huh === totally lost and impossible as SCI is fuel injected so what on earth do you have here. Carb or fuel injection ??? then next is from your first post " see fuel in the vent line from mech fuel pump so I changed that " What was that ??? the vent line or the mechanical fuel pump or BOTH. Have no idea what "that" was changed. Better explanation of all this is to get good and any real help to pin point the problem(s)

The next question is this a stock app or a modify, if MODIFIED you need to explain the fuel system and if FI what controller do you have ??
Engine serial number and year model helps a bunch to.

Is the boat up here on Winnipesaukee? If so we can meet up somewhere and you can borrow my Rinda to scan it if you would like.

Lol, that was my thought exactly, the hose or pump... just never know.

It's an SCI with throttle body Fuel injection.
There's an electric fuel pump but also a pump on side of motor. There's a clear tube from pump on side of motor that appears to be getting fuel in it from back of throttle body.
Had top ends done over last season so no lost compression
Did new fuel regulator, TPS sensor, IAC sensor
Swapped the sensor on back of distributer
No dripping from injectors
Now doing, thermostat sensor, cap, coils, plugs, wires.
It just keeps loading up with fuel.

Thanks Matt but the boats not up there yet.
Just dropped it off to mechanic to put on computer.
Hopefully he can figure it out.
See you up there.

Turns out it was the ECU

pass on my statements at this time frame good luck