The easiest way is to pull the plugs. Black = rich / white = lean and a light tan = just right.
A black dry fluffy colored plug is caused by deposits from a carburetor that is running too rich (too much gas), or excessive idling on some engines. Black smoke coming from the exhaust is a sign of a rich air/fuel mixture. The rich air/fuel mixture must be repaired before installing a new spark plug. Common causes for a rich air/fuel mixture are:
dirty air filter.
air mixture screw or carburetor needs adjusting.
choke is sticking.
carburetor float height is out of adjustment or float is sticking open.