Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 30; Flight Crew Total 4000; Flight Crew Type 500
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Aircraft
During flight instruction a noticeable engine roughness occurred. The flight was conducted under VFR and utilizing Flight Following. I immediately turned on carburetor heat to no avail and turned back toward ZZZ (airport of operations) that was about 17 nm distant.  By adjusting the throttle; rpm was kept at cruise setting and roughness stopped.  After approximate 8 miles of flight the roughness returned and would not subside.  I notified The Approach controller of the situation and asked for an expedited path to the closest airport. He cleared me direct ZZZ1 and asked [about] souls and fuel on board; with two souls and 3 hours fuel. He then switched me to ZZZ1 tower who cleared me to land.  The approach to runway was uneventful with the engine running rough but producing more than adequate power.  The landing was uneventful and taxied to the FBO without incident.
LSA pilot reported a loss of engine performance that led to a diversion and a successful landing.