I have a Murray Ultra lawn mower that starts but won't stay running. It appears to be sputtering. Any advice?

Hi,
Is this a rider or walk behind?
Peace,
Clarke

A walk behind : )

Hi,
On a walk behind mower the most common cause of sputtering (and blowing black smoke) is a clogged air filter. They can clog from just dirt buildup, or from gas or oil contamination from tipping with the filter downward.
A carboned up plug can do it, but it is far rarer and occurs over a period of years from not changing the plug
Not an end all list, just most common.
Peace,
Clarke

Thanks. Will give it a try!