1. Troubleshoot rpm's drop, found bottom cylinders #2, #3, & #4 lnop.
2. Removed and replaced (4) spark plugs with new P/N REM38E.
3. Ran up plane. Performed mag checked, mag dropping within limits.
4. Troubleshoot tack, ran up plane for 10 minutes checked tack operation system. Ops good.
All maintenance performed on this Engine was conducted in accordance with Lycoming Operator's Manual Model O-320 Series, and the ccurrent regulations of the Federal Aviation Administration and is approved for return to service with respect to the work performed.