Clean out that orange crud from the inside of the air passage and venturi. Also clean the mesh filter in the bottom of the brass tube that reaches down through the diaphragm. You will need to clean the interior of the carburetor and the main jet. Here is the Briggs manual for doing that, use the "next" key for subsequent pages:
http://recoveryvehicles.tpub.com/TM-5-4240-501-14P/css/TM-5-4240-501-14P_97.htmPart of the procedure it explains is how to inspect the diaphragm. You do not need to replace the carburetor, based on what I can see from the pictures.
