Regarding engine performance ... A frequent lawnmower problem, after a few years of operation, is that the engine cylinder head bolts lose their torque and cause inefficient compression. Look up the cylinder head bolt torque specification and snug them up ... Use a torque wrench, since some head bolts can break it over-torqued.

 

Will look in to that. I did notice the one plug is pretty carboned up and the other doesn't look too bad. I did see a second later peak from time to time and wondered if that was a misfire or late ignition on one plug.