I have a 20" Murray mower (Walmart) that has the carburetor mounted on the gas tank. It's only about 2 years old. This year it started stalling for some reason. It will start fine and you can mow with it, but then it will just stop for no apparent reason. has lots of gas. It will start again and will mow for a few minutes then stall again. I tried taking the carburetor out and cleaning it with carb cleaner, cleaned the air filter, cleaned the gas tank out, but still it keeps stalling. I thought maybe it was the gas cap, but it will stall even with the gas cap removed. Kind of at my wit's end as to what's causing this. oil level is perfect and spark plug is good too. anything else i should check?