Any time a carb sits especially with fuel in it you risk something getting clogged. I try to run some stabil through them then drain well. Be sure you verify the floats are good. Not sure what kind you have, but they can either be weighed if composite material or a gentle squeeze under water watching for air bubles if they are hollow. A bad or leaking float will case this condition. Float level is also very important. Clean the carb well blow carb cleaner through every passage (wear safety glasses)! blow air afterward. If a pressure or carb tank is available be sure to take advantage of it. That crap gums up everything. Hogwash brand is my favorite solvent.
Tony