I dealt with cleaning the carb on our A4 last spring.
First you have to determine if you have the early or late model carb. This will dictate what shape gasket you will need when putting it back together.
It is likely that the float valve may be stuck in the closed position which would not allow enough fuel into the carb. You may also likely have clogged jets which would also restrict the fuel flow.
A good cleaning with carb cleaner may be all you need to get the engine to turn over. I'd recommend removing it from the engine (2 bolts, throttle & choke controls) and working on it in your garage or workshop.
Check this page at Moyer Marines online catalog for the various carb pars you may need:
Moyer Marine Online Store
You may want to search the forums at Moyer Marine as there is a lot of info on the carb over there:
Moyer Marine Atomic 4 Community - Powered by vBulletin
Hopefully your fuel pump is working and it is fairly easy to check this out by removing the fuel connection to the carb and see if fuel comes out when you crank the engine.
Good luck.