The 138190051 Carburetor Plastic Insulator or Connecting Block is a short spacer or intake between the carburetor and the intake port on the cylinder head.
The purpose of the insulator is to prevent heat from reaching the carburetor. If the carburetor gets too hot, then it can cause fuel to quickly evaporate and vapor lock the fuel system. This is done because the intended use of the engine is on stationary power equipment that relies mostly on the flywheel fan for cooling. The insulator also features a channel matching the carburetor for the fuel bowl vent.
The carburetor insulator fits most of the 196cc 6.5hp Clone engines, including Honda GX200, Ducar 196, Ducar/Tillotson 212E, Tillotson 196R/RS, Tillotson 212R, Tillotson 225RS, Ducar/Tillotson 212E, Predator 212, and BSP 196 and 212 cylinder heads.
AKRA 2020 Rules for Carburetor Insulator
The phenolic spacer must be flat across the entire gasket mating surface, with a minimum thickness on the gasket surface .265" (not including the gasket). The gasket surface must remain parallel. No angle cutting allowed. Center inlet hole is NON-TECH(size, configuration, finish), but no rifling, grooving, dimpling, etc. allowed. Maximum mounting hole(s) size .300" NO-GO (checked with .300+ pin gauge)
Phenolic Spacer/Gasket(s) subject to spray test to check for leakage or introduction of air into the intake tract. When performing the spray test the engine may stall or speed up, both indicate that the engine has failed this test.)
NKA 2020 Rules for the Carburetor Insulator
22.214.171.124: Phenolic Insulator
126.96.36.199.1: Black phenolic insulator plate must be run between carburetor and block.
188.8.131.52.2: Plate hole and finish of plate are non-tech.
184.108.40.206.3: Fuel bleed off slot must be unaltered.
220.127.116.11.4: Thickness must be maintained at .257" minimum. The plate must be flat and maintain consistent thickness at all points.