If all the clunk tank speculation turns out unfounded...From what I have seen, the DR don't like to hold an overly lean setting. If you are unfamiliar with this motor, it might just be you are not used to it. The one's I assisted launch on tend to be very fussy about the needle... You set it to where it feels like your launchers hands will go numb from the vibration and not a tick leaner or it will flame out. It will smooth out a little after take off, but not much. In order to do this, you need a light prop like Yuri makes with enough pitch to get the flight speed you want and get that needle setting.... The glow plug also has to be up to the task, make sure you have a fresh glow plug of whatever the manufacturer recommends. FAI fuel plus maybe 2 percent nitro seems to be about max in stock config, if I am not confusing my memory with the Stalker....sorry, it has been a while .
EricV