Narrative:

Student and instructor pre-flighted aircraft. Engine started and taxied to runway per tower instructions. Followed pre takeoff procedure checklist. Engine runup was normal. 50 RPM drop on each magneto. Takeoff and initial climb were normal. At about 1;500 feet AGL about one mile from the runway the engine started to run rough and began popping and backfiring. As instructor I took control of the aircraft. Since we still had enough power to maintain flight; I began a return to the airport and contacted tower. I contacted tower and told them I had a rough running engine. [ATC was advised]. Approach and landing were uneventful.

Google
 

Original NASA ASRS Text

Title: Piper PA-38 Tomahawk instructor pilot reported experiencing engine roughness after takeoff; which resulted in a precautionary landing.

Narrative: Student and instructor pre-flighted aircraft. Engine started and taxied to runway per Tower instructions. Followed pre takeoff procedure checklist. Engine runup was normal. 50 RPM drop on each magneto. Takeoff and initial climb were normal. At about 1;500 feet AGL about one mile from the runway the engine started to run rough and began popping and backfiring. As instructor I took control of the aircraft. Since we still had enough power to maintain flight; I began a return to the airport and contacted Tower. I contacted Tower and told them I had a rough running engine. [ATC was advised]. Approach and landing were uneventful.

Data retrieved from NASA's ASRS site 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.