It is normal for the floats to evaporate because they are open to atmosphere. This should take longer than a few days with the air cleaner installed. Remember, today's gasohol is not yesterday's gasoline.
More importantly, if your fuel pump is losing its prime, the fuel line is dry which certainly causes a hard start. Check this by pouring some fuel into the carb throat after a few days. The engine should start up immediately.
Where is the fuel going? Is it a slow diaphragm leak back into the timing cover or is it simply back-washing to the tank? You can bench-test to know the answer before throwing parts at this problem.
If fuel is back-washing to the tank, a simple check valve at the frame hose will keep the pump 'wet'. - Dave