Hachi, make sure that you have replaced the governor rod into the
correct hole in the throttle lever. Make sure that you can visually see
the throttle responding to governor inputs. The governors are usually a
stone age simple centrifugal force type using spinning weights to move
the governor arm which in turn is connected to the throttle. When you
take any carburetor apart you must use compressed air to clean it out
for sure. Carburetor cleaner sprays won't have the required pressure to
accomplish the job. I've seen that mistake made too many times. Use a
cleaner that contains the chemical "toluene". It will remove gum and
varnish like no other. Make certain that the needle and seat valve is
not leaking. You can usually check this by gently blowing air through
the fuel intake passage with the needle seated (carb inverted) making
sure it's not leaking air. Make certain that you have set the correct
float height to specification. If that is not correct, the engine can
either be starved or flooded with fuel. Replace the in line fuel filter
if it has one, along with any air filtration and you should be good
IMHO. Good luck.