The spark plug in the picture has been partially cleaned. Readers can tell that it was very dirty and corroded. It probably was not delivering a very good spark to the engine. How to know if a spark plug is bad on a snowblower? In situations such as this the engine will be difficult to start and may also run roughly. These symptoms can also be caused by dirty gas, a dirty carburetor or clogged filters. You really have to solve the problem through a process of elimination and the easiest one is to check and clean the spark plug first. Don’t forget to set the gap properly each time you clean the spark plug.
Remove the spark plug after first removing the spark plug wire. Next clean it up using medium grit sand paper. If you cannot get all of the grit off, it is sometimes just easier to install a new plug. Make sure that the gap is set properly as well before you test it.
The next step is to reconnect the spark plug wire. Hold the plug using gloves with the metal portion touching the side of the metal housing of the engine. Slowly crank the engine and observe if a spark is being generated between the central post of the spark plug and the outer metal housing of the plug. This test will confirm that electricity is being delivered to the plug and it is generating a spark.
Reinstall the plug and start the engine. If the engine still does not run smoothly, you may need to clean the carburetor and filters. Before doing so make sure you have gasoline in the tank! This is actually a common problem for many people who have trouble starting their snow blower. They forget to add gasoline!