No, put the shim into the carb. The press the o-ring into the shim. It gives a rubber mating surface fully around the circumference of the intake manifold, so the whole round end is sealed to the carb
The shim fill the space around the intake so it can clamp on, the o-ring is smooshed between the intake and carb throut.
Wouldn't worry about it untill you diagnose your problem tho...it could also be a Piston pin clip that flew out and trashed the cylinder.