Idle problem, 310HP Carb, Sometimes

Sometimes my 2001 Mobius 310HP Carb motor idles real bad then stalls. Other times the boat runs perfect all day. What could cause such varied performance like this. I run 91 Octane gas only. I am 99% of the time always at the same lake. Could I be getting water in the gas? I just had my boat serviced and have been out 4 times since. 2 times the boat ran perfect. 1 time I had real bad problems with it stalling while trying to pickup a fallen rider at idle or no wake speed. The other time It just had a little harder time starting, I had to feed fuel everytime to start when normally I don't have too. Any ideas?
Thanks

I have had the same problem. I adjusted the idle up a little and it seems to have worked. I have a 2000 Kanga and the same Indmar 310 engine