I have a riding mower with a Tecumseh OHV125 engine. When I turn the key it tries to start, but barely. I've tried it with a battery jump start machine attached which states there is sufficient charge in the battery. I just replaced the starter and still nothing. Please help, the grass is outgrowing me.

Tecumseh are known for valves not seating. You may need to pull apart and check them. Check the bascis first like air and fuel filter