This lawn mower has had every single part replaced because the ignition switch went bad and shorted out the entire electrical system.Now it seems to have a problem with the fuel,it will run then will smother out.We changed the fuel filter so this isn't the problem.Can we add a gas additive to help clean the lines?

Don't add any additives to an engine that isn't running right, it will confuse some symptoms. If you think your lines are gummed up just switch them out. I would start by opening the carb bowl and clean and inspect, needle valve too. Make sure the needle shuts the fuel off when the float is raised. Smother out could be flooding but it could also be the coil breaking down and not firing the spark plug. Lets start with the bowel and come back with your results.

Ball has hit the nail on the head, let us know what happens.

Had the same problem. Plus would run then just quit, no spark. Removed flywheel and found the magnets came off flywheel and stuck to the mag . Cleaned all parts and use epoxy to glue back on, mark the spots they came off. Now it runs fine. Hope this helps. I thought mine was coil to but glad I took the flywheel off before I spent $50. But if your getting spark then yes ball is on the mark. Good place to start.