Seafoam has worked for some, but if the carbs weren't drained of fuel during the winter, there is probably more build-up of residue than seafoam can take care of. Might be worth a shot. Cleaning / replacing carb parts (rebuild) is finicky, but if your fairly handy and get good directions, it's doable. After the cleaning of tiny ports and replacing of jets and needle valves and carb floats, the next tricky part on your engine will be syncing the carbs and the adjustment after you're finished rebuilding them. Usually requires a special tool with a gauge for each carb to sync them properly. You can make one yourself. I enjoy doing battle with my outboard, if you don't, go to the pros.
The other advice to check fuel line restrictions is good too.