Most of the box store mowers, Cub cadet, JD, even Toro are MTD mowers. Junk. Go to a small engine dealer and get a good brand. Like Ferris, Scag, Grasshopper.
Pull the air filter and make sure there is no dirt residue in the carburetor intake. If there is, the air filter was not seating properly and you might need new rings. Otherwise check the head gasket.
Grasshopper front mount is what I suggest for getting around trees. The deck tilts up for easy maintenance. They are built like a tank and ride way better than a Scag.
A lot of times if you take the carburetor bowl off the nut that holds it on has some wholes in it that get varnished over. Clean the bowl and the nut, and the main jet if possible. Run a small piece of wire up into the main jet to loosen the varnish. Or take it out with a small screw driver...