It is a good practice to replace the spark every year. This will prevent problems from arising when the snowblower is in use. Alternately, you can change spark plug when the snowblower is used for approximately 100 hours. It is a decent idea that spark plug can be cleaned every 20 to 30 hours to check the condition and make sure gap is appropriate. You'll be able to check the signs that spark plug needs to be replaced, and you can avoid dirt buildup.