This linkage kit will enable you to convert your single HS4 from using a waxstat jet to using a standard fixed jet. The waxstat jet works well when it works- but they have a reputation for random failures, and are quite expensive, so many opt to use this kit to allow use of the more reliable fixed jet. The jets use completely different linkages, but are otherwise interchangable, so this kit is all that is needed, besides the jet itself.
 
You will also need to get an AUD9451A jet assembly, or if rebuilding the full carb a CRK121 master kit.