Airplane: Piper Warrior II (O-320 engine)
Airport: CYGK (north shore of Lake Ontario
Weather: CAVU; 15°c OAT; prevailing westerly winds, but airport in local light lake breeze from the south
About five miles back from landing today, I noticed the engine running rough whenever I reduced power — it was fine above 2,200 RPM, but started vibrating at any lower setting, enough that the plane (carbureted) shook noticeably. I accepted the vibration, landed, and taxied to the ramp, with the plane still shaking. I switched mags while taxiing and tried different mixture settings, with no difference. When I tried to shut down with the mixture lever, the engine kept running (even at full lean), and I had to stop it with the mags.
Your diagnosis? (I’ll post the answer in a day or two).