We get people ask is my engine an EX21 or KX21
The engines use the same bottom end or short block except the EX21 still uses the governor and has a shaft sticking out the top of the block under the fuel tank.
The EX21 we have dismantled to take pictures has EX21 cast into the cylinder head.
The carburetor on the left is from a KX21 subaru go kart engine, it has a larger fuel bowl and the fuel bowl is aluminum not pressed tin like the EX21 fuel bowl.
The easiest way withought removing the cylinder head from a KX21 or EX21 is to remove the rocker cover and have a look at the camshaft to cylinder head mounting location. The KX21 has a narrow section where the camshaft mounts to the head opposite the valves. The head on the right is an EX21 head and you will notice the cam mounting bed opposite the valves is far wider.
Note the cam bed on the EX21 cylinder head is far wider than the KX21 cylinder head.
The difference internally once the cylinder head has been removed is the valve size and the combustion chamber size. The KX21 close chamber on the left and the EX21 on the right with its open chamber.
The KX21 cylinder head on the left has a larger and is different in shape to the EX21 subaru cylinder head on the right.
More Pics and Info to be added shortly