Poulan 521 Single Stage Snowblower 136cc Recoil OHV (21) #961880007Poulan 521 Single Stage Snowblower 136cc Recoil OHV (21) #961880007. The Poulan 21-inch single stage snow thrower features a Storm Force 4-stroke 136cc engine that delivers powerful performance and effortless starting. The 21-inch auger width and 13-inch auger diameter make short work of compacted ice.