Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Sounds like one side of the engine may not be firing if it is running unevenly. While mower is running pull each plug individually, and see if mower stays running each time a plug wire is pulled off. If you pull one side and mower dies, the opposite side is the dead side. Also pull valve cover and check valve clearance and also the push rods for bends or disconnect
Let me know if I can assist any further