Hi!
To me it sounds as if you run too much nitro!!
Engines developed for low nitro fuel behaves like you describe...sudden stops at all throttel settings and general erratic engine behavior.
Try 5% nitro and an Enya 3 glowplug.
A uniflow tank is what I recommend, it has two clunks running parallel to each other, with one hose a little bit shorter than the other.The long hose is going to the carb, the short one to pressure nipple on the silencer.
But the best tank available is the Tettra "bubbleless tank". No air bubbles could get into the fuel if you use one of those!

Regards!
Jan Karlsson
Sweden