Small Engines (Lawn Mowers, etc.): Does not run, suction tube, gas tank

Question
I have a Yard Machine Briggs%26Stratton, 3.5H, 20".
When I push the bubble to give it gas, no gas is feed to the carburetor, when put some gas manually, the motor starts easily, but stops very soon, because no gas is feed.
I need to know why the the bubble does not feed gas and a little  explanation how the gas is feed to the carburetor.
I will appreciate your answer

Answer
If this is the engine with the carburetor mounted to the gas tank, the problem is either the suction tube is clogged or the diphragm is bad. When you push on the primer, the air is pushed out of the primer, and when you let go it draws fuel up through the suction tube. The next time you push it you push the fuel out of the primer into the engine and draw more into the bubble.