I have a basic 21" 4hp walk behind mower . MTD purchased at Home Depot. It has been sitting indoors for 2-2.5 years with some fuel inside. It does turn over but doesn't even cough. Any reasonable way to start it?

I would suggest getting rid of any old fuel in it, as that is too long for old fuel to be in it. Also, I would change the spark plug or clean the gap in it with sandpaper or a file.

I am not a lawn mower expert. But, I have experienced what you are trying to do.

Hopefully, concerning more particulars to your problem, their will be others who will answer who can give you an answer in more detail.

Clough is correct. Empty all fuel and put in fresh. I would even change oil and clean carb as old fuel will cause a varnish type film inside it and close or restrict openings.

Have You Checked To See If You Are Getting Fire Through Your Spark Plug?