You have a problem that used to be pretty common with weed eaters and chain saws here in the 'States. Some years back if you failed to run the carbs dry and flush them with alcohol prior to a seasons' storage the same thing would happen, along with the rubber tip on the needle rotting away.

Flush the carb with isopropel (rubbing) alcohol just before you are going to store the plane for a period of time. Just obtain the easy, over the counter stuff and it will work fine.

Pat