Small Engine Parts Specialists
Note: This is a great video for taking your carburator apart.
The only thing I would add is that it is
definitely worth the time
to take the carb off the machine to work on it.

Notice at 3:30 when he's got the carb upside down. What I
always do at that point is blow air (with my mouth) in the gas
inlet on the side of the carb. In this position the float is shutting
off the needle valve and it should be
perfectly sealed. If you
gently lift the float up you should hear the air going through.
This is extremely important since a leaking needle valve won't
stop the flow of gas completely and will make your carb
overflow and drip on the floor.

Ideally you should replace the needle and seat with every
tune-up job. When installing the seat (the round rubber thingy)
I use a 3/16" round file and tap it good all the way down in the
hole. I then install the float and needle valve and do the seal
test again. It's worth doing it right the first time if you want to
save the agravation of taking it all apart again later on.