Could be carb orator issues or if the engine is cold it might not start or a stuck valve not letting enough gas coming in to the engine or exhaust valve or check your valve push for the right clearance. Hope this helps Cody
When was the last time you used your mower? It is possible that the fuel has gone stale. If this is the case you will need to drain the fuel from the engine and clean the tank and carburetor with some carburetor cleaner. Then to finish, add fresh gas that has been treated with Advanced Formula Fuel Treatment and Stabilizer.