Backcountry-
Very early on during my initial flight testing (something like the third flight or so with fall temps like we are having now) I had something similar happen during takeoff. I was climbing out and had a sudden loss of power and a rough running engine accompanied by a slight whiff of fuel. I pulled the throttle back a eased it back in little and things seemed to smooth out up to about 3900 rpm ... so I made it around the pattern and landed. My initial thought was vapor lock from the winter auto fuel ... but I was not on the ground that long, plus it was a cool day.
Upon landing, I downloaded the Dynon SkyView's recorded data to a flash drive and looked at the data in a graph generated by Savy. It was easy to see what happened ... during the initial onset of the "event" the left EGT got cooler than the right, RPM dropped from 5250 to 4000 ish, the fuel pressure dropped a little and fuel flow increased a little. By all appearances the left carb went rich.
Removed the left carb and there was nothing in the bowl, floats were just fine ... so I removed the float arm and needle then turned on the electric fuel pump so I could flush a little fuel through the system and found what appeared to be a tiny grain of sand appear in the fuel containment container. I'm guessing that tiny piece of grit kept the needle valve open and allowed excess fuel to enter the bowl making that carb go rich ... I have not had a reoccurrence since.
Using Savy really helped me get a clue as to which side of the engine needed the attention ... suggest you may want to analyze your flight data ... it may help get you pointed in the right direction.
Happy flying,