M20E pilot reported landing gear-up because of distractions dealing with an engine problem.

Attributes
ACN	1096562
Time
Date	201306
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	M-20 E Super 21
Operating Under FAR Part	Part 91
Flight Phase	Landing
Route In Use	Visual Approach
Flight Plan	None
Component
Aircraft Component	Engine
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Instrument Flight Crew Private
Experience	Flight Crew Last 90 Days 5 Flight Crew Total 780 Flight Crew Type 80
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy Ground Event / Encounter Gear Up Landing

Narrative:

Following standard briefing from flight service; system checks; and run-up; departed and initiated climb to the northwest. As I climbed engine began running rough. I changed fuel mixture and switched fuel tanks. Engine continued to run rough and produce only partial power. I decided to return to airport. On short final I set flaps and adjusted trim to landing configuration. As I approached touchdown; I realized gear-up warning alarm was sounding. I moved landing gear lever to down position. However; it was too late for gear to fully extend and plane touched down on runway and landed with gear up. Notified unicom that I landed gear-up on runway and that there were no injuries. I shut down all systems on the plane and exited. At this time the cause of the engine problem is unknown. One possible cause is that an injector became plugged causing the partial power. The primary cause of the 'gear-up' landing is not following landing checklist under all landing conditions.

Original NASA ASRS Text

Title: M20E pilot reported landing gear-up because of distractions dealing with an engine problem.

Narrative: Following standard briefing from flight service; system checks; and run-up; departed and initiated climb to the northwest. As I climbed engine began running rough. I changed fuel mixture and switched fuel tanks. Engine continued to run rough and produce only partial power. I decided to return to airport. On short final I set flaps and adjusted trim to landing configuration. As I approached touchdown; I realized gear-up warning alarm was sounding. I moved landing gear lever to down position. However; it was too late for gear to fully extend and plane touched down on runway and landed with gear up. Notified UNICOM that I landed gear-up on runway and that there were no injuries. I shut down all systems on the plane and exited. At this time the cause of the engine problem is unknown. One possible cause is that an injector became plugged causing the partial power. The primary cause of the 'gear-up' landing is not following landing checklist under all landing conditions.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.