My DLE-20 started to run really rough this past summer and I couldn't accelerate it past an idle. After checking everything obvious I took the carb off, and found these wedged in the reeds:
It was a couple of pieces of epoxy that had held my ballast weights on. These two must have vibrated loose. After a little cleanup the engine ran fine.
I'm not suggesting that this is your problem - but it was a lesson to me that the source of your problem may be where no-one expects.