I have a 4hp B&S Quantum lawn mower. It's old but runs well. I have had difficulty starting it for about a year. If I spray starter fluid in the carb or the cumbustion chamber it starts right away and runs until I shut it off. I noticed that the choke plate does not fully close when the choke is engaged. When I pulled the air cleaner and assembly off, the spring that should close the choke plate seems to be attached improperly. Is there a diagram somewhere that shows how it is supposed to be assembled?
The choke is 'spring'loaded closed by the carb diaphragm located between the carb and the tank. It's pulled open by manifold vacuum when the engine starts.
Start by replacing the diaphragm. It's probably perished.
phil_saunders(a)bigfoot.com
Phil Saunders
March 2010
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