Good morning. I have a Honda GCV 160 self-propelled 21" lawn mower that I purchased 4 years ago. Today while mowing it stopped cold. It did not sputter or run rough before it died. I have used Tru Fuel 4-Cycle fuel since I purchased it and I change the oil and spark plug each year and it has always started with 1-2 pulls. I haven't changed the air filter for a couple of years. I just pull it out to knock the dust off and blow on it. The engine will not start at all when I pull the cord, which pulls normally. It does not even attempt to start. Any thoughts on possible causes? Thanks.