LB's advice about "Aggresively lean on taxi is good" .When others (usually a cross-hire or flying school) used the aircraft, I had mag drop issues which were usually cleared by high RPM runups, leaned for max RPM and left for 45-60 second until reducing revs for second mag check. I attributed this to poor leaning in taxi.
I had a fouled plug on an O-360 at about 400 ft after takeoff - still climbed ok, but really rough running. Underpants were in danger territority. Quick PAN call and early turn to downwind with a very tight base leg for an uneventful landing. $150 coffee at Rottnest canned and I replaced the plug.