I had the same boat. 89' Combrio. I never had the issue you are having but I did have to rebuild the carb a couple of times over the 24 years I owned it. I always return to the basics on a carbureted engine: You need, fuel, air, compression and fire. When its in the water, remove the spark arrestor and crank it over and see if any fuel is leaking down the overflow tubes in the carb. if it is, your float is sticking open due to a bad float or dirty/wore needle and seat in the carb.
If not, advance the throttle once and see if you get a nice spray of fuel. If so, try cranking it and if it doesn't fire, then check the spark. Moisture in the fuel can do what your talking about also.