Agree.I wouldn't go ripping into the carb yet. If it runs ok once started I'd exhaust some other mentioned items first. Lots of ideas here already shared.
OK easy breasy. This is definitely fuel bleeding down and out so the fuel pump is having to ketchup. You've either got that or weak fuel pumps/pressure. Like some others have said, I'd replace the fuel line with good marine ethanol rated line, don't got cheap, that includes the primer bulb and filter because why not. This is an easy task. Run it and see how it goes, if issue remains then you've got weak fuel pumps. Also, be sure the vent on your tank is functional, could be vaporlock creating a bit of a vacuum which the pumps are strong enough to overcome at high RPM but tougher to combat while cranking.Understand that I'm new to boats as I just got this a few months back. It has a 94 Mercury Mariner. The choke activates when you push the key into the ignition. Once I've gotten to my fishing spot and fish a while, I go to start it back up and it just cranks but never starts. Then it'll start momentarily and shut off no matter if I raise up the idle lever. I just have to sit there and give it some time and it will eventually start and run good again after it starts.