To check the spark plug on a snow blower, disconnect the spark plug wire, remove the plug from the snow blower, reconnect the wire to the plug, and hold the plug with insulated pliers. Verify the presence of a spark at the end of the plug while starting the device.
Inspect the end of the spark plug for dirt and debris. Over time, carbon deposits accumulate on the electrode, which can prevent it from sparking. Clean the end of the spark plug with a fine wire brush to remove the carbon deposits.
Check the end of the spark plug for wet, black and oily deposits. Oily deposits are a sign that oil is leaking into the cylinder past worn piston rings or valves. Wipe any oily deposits off the spark plug with a rag.
Verify that the electrode isn't excessively worn or eroded. If the electrode does not have uniform thickness, the spark plug is probably no good. Ensure that there are no chips or dings in the electrode. Damage to the end of the spark plug could indicate a more severe problem, such as loose material in the cylinders.
After performing these inspections, reconnect the spark plug wire to the spark plug, and once again check for a spark while starting the snow blower.