This video really resonates with me because I had a similar incident in my Nanchang last week.I was leading a 4 ship formation and My troubles started with a mild RPM oscillations. So I went to full rich, scanned the gauges, which were normal and then turned the formation towards our home airport which was about 15 miles away. As soon as I had finished the turn the engine stumbled. At this point I declared an emergency, detached the 2nd element and started a slow climb. My wingman stayed with me a reported no leaks or smoke.
For the first half of the trip the choice was fly over the city or around the edge over water, so I obviously stayed over the water. As we chugged back home the engine was intermittently stumbling but still maintaining power. At this point I decided not to touch anything on the theory that I didn’t want to mess with what was working. I told the tower I was doing a straight in on the runway that was basically aligned with the track back to the airport and starting to feel relatively sanguine when the engine without warning quit cold. I was startled enough to do nothing and after maybe 2 seconds the engine roared back to life. It ran for maybe 5 seconds and then quit again. Again I froze for a second and the cycle repeated itself. The third time with no action on my part the engine stayed running. At this point my attention was totally outside planing on where to put the airplane.
Fortunately the engine stayed running and I was able to maintain height until I could made a steep glide approach and an uneventful landing at our home airport with CFR assets standing by. The engine was running at idle as I rolled out after landing but quit as soon as I tried to add power to taxi off the runway.
if the engine had just quit I knew exactly what to do, however intermittent loss of power with no obvious indication of what is wrong is a very difficult situation to deal with. I think I made the right decision not to adjust the engine controls except to go to rich mixture but it is hard to say. The smartest thing I did was as soon as the engine started acting in an odd way I turned towards the airport and after the first stumble declared an emergency and arranged my flight path to cater for a total failure at anytime