A-B1710366-AI CUP-FLYWHEELOne New Aftermarket Replacement Cup Flywheel Fits Briggs & Fits Stratton Small Engines This flywheel cup (also called a recoil starter cup or starter drive cup) mounts on the flywheel and engages the recoil starter mechanism to crank the engine. It is a common wear and failure point on walk behind lawn mowers and other outdoor power equipment when the cup is cracked, worn, or broken, the recoil starter will not engage and the engine cannot be started.