How are the springs set up on the carburrttor on the Briggs and Stratton 35?

Just got myself a second hand Briggs and Stratton 35 Classic Lawnmower. Bought in an auction and its in really good nick. Trouble is when I start it it just keeps surging. The were 2 springs attached loosely to the carburettor and whilst these are new they do not appear to be under tension at any time. Where can I get a correct new set of springs and can someone help with a diagram of how they are supposed to be fitted.
Any (constructive) help or advice will be greatly recieved.