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All Walbro carburetors that have chokes will drip fuel, especially when at or near idle.
This is because a 2-stroke engine "spits" at the carburetor. This is caused by the rapid opening and closing of the reed valve. A small amount of fuel is forced back out the carburetor, hitting the choke butterfly valve, running down the choke valve shaft, and out. As the engine speeds up under load, the back-pressure wave from the reed valve has less time to reach the carburetor opening so fuel leakage is less.
Sealing the airbox flange with RTV cement, for example, will only help a little. Thankfully, fuel leakage is only annoying but it is not harmful or dangerous. For the obsessive-compulsive: put a blob of 5-minute epoxy over the lower shaft end of the choke valve. Be sure to use brake cleaner to thoroughly clean the area around the shaft end of any oil. It might last a while before falling off but the carburetor will not drip in the meantime.
If an engine has hundreds of hours on it, the carburetor can be worn out. In particular, the throttle valve shaft bushings may be worn out and the carburetor will leak air and/or leak a lot of fuel. The other part of the carburetor that wear out is the inlet valve needle seat. Both of these issues require that the carburetor be replaced. These problems are discussed on this page.
2-stroke engines are messy and inefficient -- but we like them anyway because of their high power output to weight ratio.