I would normally agree with the Full up with the fast idle lever, and hopefully uncle Al ore TurboD can confirm / correct me on this but some of the Mercriners of the time didn't have a choke as we know it, but used an "enrichening valve" which basically throws more fuel in rather than cutting off the air.
Net result nobody can start my engine 'coz the last thing you want to do when it's cold is un- choke it again by opening the throttle with the fast idle lever....... Not intuitive.
As I have no idea what type of carb your engine has, once you get the lid off, have a look at what the choke solenoid does - if it moves a flap across the intake, use the fast idle. if it moves some tiny lever at the top of the carb with no air valve movement, make sure the fast idle lever is all the way down.
As for the lid, the front panel should come off either with a twistlock on the front at the bottom or a catch hidden underneath. panel falls off, revealing two or threee clasps that hold the sides together.... Just be careful in a high wind!