Small Engines (Lawn Mowers, etc.): Honda G400 small engine, sediment bowl, air holes

Question
Hello  My G400 has been sitting in storage for about 10 years. Took carb off and cleaned needle seat, sediment bowl and main jet.  Changed oil etc.  Starts fine (no smoke), If I slowly bring throttle up it gains rpm as normal.  If I bring rpm faster engine stumbles and runs rough puffing black.  I removed the air filter and condition improved but not entirely.  Plug is also old.  Power plant runs a centrifugal pump, and my concern is that once under load and governed, the condition will persist  thanks for your help

Answer
It sounds like the carb is running too rich, too much fuel.  Did you blow compressed air from an air compressor through all the carburetor orfices when you had the carb apart?  There are some very small holes, in the carb throat, on the inside of the carb throat, closest to the engine intake.  These are your high speed circuit holes.  Make sure they are clean as well as the carburetor air holes on the air filter side of the carb.

Let me know if this helps.

Eric