On top of the shroud it will have a model number, either W1-145 (4hp, 4cycle), W1-185 (5hp, 4cycle) or WT1-125 (4hp, 2cycle). Of course those horse power ratings aren't totally accurate but those are the three WR models of the white-engine vintage...at least that came on the snapper walk-behinds. Parts are not easy to come by other than the air filters. If any of the online parts suppliers can't help eBay is usually the best place unfortunately. Or find another WR engine for parts. Sad really, those are great engines and last forever. Really sad to see something so well built go out of production.