Good old Mariner.
They don't have a choke plate on that motor. It's got a knob on the front of the motor that you pull out, also turn to adjust idle speed. I hated them and I'm glad I don't have to deal with 'em anymore! I want to say its' set up sort of like a prime-start but I don't remember. I try to block out Merc and mariner knowledge.
If it is prime-start (no choke plate), it could be a clogged passage in the carb and/or it's bowl.
Also on prime-start motors, the proper way to start a cold one is no throttle, just crank. Opposite of a "choke" motor where you'd advance the throttle a little and then crank it with the choke plate closed (on).
Also on prime-start motors, they can be a real pain in the neck if passages are plugged. Sometimes you can't get to the plugged passage to clean it, which is the case on a particular Yamaha I'm working on at the moment.
Reason for prime-start is because that and the Merc equivalant had the forward-reverse shift in the tiller handle. It's convenient--until you have to work on it, then it's a pain in the neck. Because it shifts as soon as you move the tiller grip, there's no throttle in neutral so a choke plate style carb would've been hard to start anyway, thus they put a prime-starter on it which gives them a selling point...no choke AND shift in the throttle grip.