I just started flying a 4 star and Im experiencing the same sort of thing. Make sure it rolls relatively straight at low throttle (or just roll it with the engine dead). It will try to go left as soon as you give it throttle ( I mean immediately). I am still having trouble, but I have found that if you give it just a touch of right as you throttle it up it helps. Just let up as soon as you see it starting to go right. Give it throttle slowly and dont over correct, that is my problem. I have managed to take off with out running off the run way the last few times. I still am not that good at it. I know the principle, but reaction is a different story. I guess practice makes perfect.