This kit makes the carbed 600 fly and gives the bigger bore sleds fits in the trails. We made this kit backshift much better than stock as the oem calibration is quite lazy in on/off corner to corner riding. The better backshift and hard corner to corner acceleration make your 600 act like its got big bore smoke. The kit includes detailed instructions for 120-137" models and tracks from 1" up to 1-3/4", and settings for elevation changes as well. Kit includes: Primary spring, secondary spring, Hot Rod Sled Shop pin kit, and progressive helix. The kit was designed to use the stock 412 Ramps.