Hello, I am working on a Briggs and Stratton 18 HP Vanguard engine in a 10k generator. Model number 356445 0208-G1 10110311. Engine runs lean, it surges slightly and the spark plugs are practically white. If I close the choke slightly it clears up nicely. The generator is ten years old with little use. So far I have drained and flushed the fuel tank and line, it wasn't terrible. I then removed the top half of the carburetor and cleaned the pilot jet, main jet which is located in the side, and removed the float and needle to clean the seat. I blew out all the passages and cleaned the float bowl. Overall the carburetor wasn't that dirty or corroded. Reassembled and filled tank with non-ethanol 92 octane fuel. Still runs on the lean side and again closing the choke slight makes it run so much better. I have drilled out jets in the past but was wondering if anyone has any first hand experience with this concern with this engine? It does a have an idle adjustment screw with a plastic lock on it that I haven't touched yet. So any input would be greatly appreciated. Thankyou!