Sounds to me like the low end needle is not adjusted properly. Since you are flying it already it's probably broke-in, maybe not all the way but close.
The low end needle is a mystery for many modelers, it shouldn't be. The next time you go to the field, tune that low end needle, here's how.
Start the engine as you always do, let it warm up, remove glow heater before tuning high end needle(always), tune the high end needle as you would anything else. Next your going to let engine idle as low as you can without stalling and pinch the fuel line off as close to the carb as you can. LISTEN..... Did it rev up before it stalled( I bet it did). That means the low end needle is to rich and throttle responce will be very poor. Lean the low end needle 1/4 turn. Restart, and tune high end needle again. Now repeat the fuel line pinch again, listen. If the engine idles with no change and quits abruptly, it's perfect. If the engine slows down and then dies you leaned the low end needle to much, richen it back up.
My guess is you will have to turn the low end needle more than 1/4 turn either way to tune it properly, just remember to retune high end needle after every adjustment. This will ensure the proper amount of fuel is being delivered to the carb in the first place, therfore giving you true readings.
Re-cap; Pinch fuel line off at idle, engine revs before stalling, low end needle is to rich.
Pinch fuel line off at idle, engine slows to a stop, low end needle is to lean.
Pinch fuel line off at idle, engine idles fine then stalls abruptly, low end needle is perfect ( haven't had one do this yet, it's hard to get one perfect).
This will improve your throttle responce to instant. And flame outs will be something of the past, it's like a whole different engine .