The 138190029 Clone Lash Cap (Valve Rotor) sits on the exhaust valve retainer on the 196 clone engines. 

The valve lash is used to prevent wear on the valve stem and manage head transferring from the exhaust valve and port to the valve train. Valvetrain weight is significant for racing or performance engines. Unless you are required to run a lash cap because of the rules, we suggest not using one or at least using the lightest weight one available. These lash caps average around 2 grams, and every gram on the valve side is worth about 40rpms. 

These are the OEM Replacement Exhaust Valve Spring Retainer for 196cc 6.5hp GX200 Clones, including the Tillotson 196R/RS, Ducar 196, and Box Stock 196. 

AKRA 2020 Rules for Lash Caps

Lash caps on the exhaust valve only.

NKA 2020 Rules for Lash Caps

40.4.20.4.10: Lash caps on the exhaust valve only. Intake retainer must retain stock appearance –no length or thickness check. The material must be magnetic.