I too suffered from same problem on low end. A small adjustment to idle mixtured fixed that. I also had the plane die during full throttle after 3-4 minutes of flight..... As it turns out the best and first thing I should have done is put a fuel filter in between the take and the main needle. I found that small particles were being drawn up after running for a bit and cutting off fuel flow and resulting in an overly lean condition that usually resulted in me making a dead stick. As soon as the engine died, the particles returned back to the tank or floated around.

After adding the filter and cleaning out between it and the carb, all has been great.

Just a thought.

Cheers,

VG