Small Engines (Lawn Mowers, etc.): carbureter, briggs and stratton, hp 3600

Question
I have a Dynamark - Model # 4218-2500 - Serial # 673388 -
Code # 6349 with a Briggs and Stratton - Engine Model
#422707 - Type 0157-01 - Code 86103012 - 18 hp 3600/min
(SAEJ607) Twin Cylinder Magnitron. It seems to be getting
too much air in the carbureter. I can start it but only if I
block the carb when I turn the key. Can you tell me what is
wrong

Answer
Is the fuel pump working?  I'd start by removing, dis-assembling and cleaning the carburetor with compressed air from an air compressor and spraying carburetor cleaner through all the carburetor orfices to make sure none of the orfices are clogged.  

Those carbs are pretty simple and do not require any special tools to rebuild them.  Have you checked You Tube for videos on rebuilding or cleaning riding mower carburetors?

Eric