I have a 3 cylinder 60 hp 2 stroke merc. that doesn't like to start at the begining of the day. I have to crank it for 10 to 20 minutes before it'll fire up. Once it gets started it runs fine for the rest of the day. I've just replaced the plugs but that didn't help any.
Could be that it's not getting enough electricity for one reason or another. Could be a bad battery or bad connection. I had a similar problem with my inline 6, when I added another battery it starts like new.