Small Engines (Lawn Mowers, etc.): carburetor cleaning, air vent, float bowl

Question
I have a 3 year old craftsman lawn mower.

Can you explain in detail about how to Clean the Carburetor.

I change Air filter every year. There is a small plastic tube in the hole where Air filter is plugged. What is the function of that tube?

Answer
The tube is an air vent to allow the fuel bowl to match atmospheric pressure.

To clean the carb you will need to dis-assemble it; mainly just removing the float bowl nut, bowl, float and inlet needle.  Normally all we do it blow compressed air from and air compressor through all the orfices in the carb. There is the main fuel tube that runs up through center of the carb, the float bowl nut orfices and the orfices in the ventri side, the air filter side, of the carb.  

If the carb has severe build-up we will remove the primer bulb, butterfly shaft and soak it in some strong carb cleaner.

Does this help?
Eric