...the easy way
Manufacturers recommend you flush your small outboard through with fresh water after every use. One way to do this is to fill your wheelie bin with water, clamp the outboard engine to one side and start it up. After a minute or so, turn off the fuel tap and let the engine run ’till it stops, which will drain the carburettor of fuel, making it less likely to gum up.
The best bit is this will clean your bin out too!