I'd pull the plugs, clamp off the fuel line, and see if you can turn the engine over by hand, or with the battery. That would make sure the engine or pump isn't locked. It would be a good idea to check the compression at this point also, if it is turning over OK, to give you a good initial starting reading for future reference.
I would also clean the carbs before you try to start it. If they have been sitting for 3 years with fuel, they will definitely be gummed up. This also goes for the fuel filter.
Check oil lines etc.. Rubber lines can dry out and crack. Consider going pre-mix if not already converted.
Good Luck!