Small Engines (Lawn Mowers, etc.): Briggs & Stratton, surging briggs

Question
I have a 9hp vertical powerbuilt B&S(model #28b702,type 1.154-E1 that seems to be (hunting) idles up and down.I've checked the gas,air filter,fuel line,muffler,and the crankcase manifold (pcv).What's next?

Answer
Most likely the carburetor needs to be rebuilt.  Probably there's a bit of dirt somewhere keeping fuel from flowing properly.  It could also be a leaky gasket,  but usually it's just from dirt and varnish.  You'll probably need to soak it in a soak can, spray cleaner is only about 50% effective.