Many engine performance problems can be linked to maintenance issues such as stale fuel, dirty air filter, fouled spark plug, and deteriorated oil. A great way to help avoid these problems would be to perform an annual tune-up using a Briggs & Stratton Engine Maintenance Kit.
Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.
If you wish to perform this maintenance yourself, a good source for engine specifications and technical servicing information would be a Briggs & Stratton Repair Manual. The correct Repair Manual for your model engine is often listed in your engine's Illustrated Parts List. Repair Manuals are available for purchase from a Briggs & Stratton authorized dealer. Your Illustrated Parts List will also provide component part numbers specific to your engine's Model, Type, and Code that you may require.