The fuel inlet needle valve is leaking - probably due to dirty fuel. Remove carb bowl and float, and clean needle and seat. The leaking valve is allowing fuel to run down the manifold and into the engine whilst at rest. Confirmed if the fuel level seems to drop when not in use, and/or it can be started with no choke/prime from cold.
This is NOT a major strip down job - worn rings will produce low power and LOTS of blue smoke before getting to this stage.
phil_saunders(a)bigfoot.com
Phil Saunders, January 2011
