The engine is a turnigy so you have that working against you from the start.
Most new engines won't realize real good transition until after several tanks of fuel.
Trouble with transition from idle to mid-range is typically the low speed needle setting or it can also be bad geometry with the mechanical throttle linkage.
If you watch the carb butterfly as you increase throttle it should be moving immediately with no delay or dead spots. Sometimes you have to program a throttle curve to smooth it out.