The problem is not that the nose drifts to the left, the problem is when I try to turn it back using the rudder stick it doesn't respond until I reduce the throtle
Do you have any idea what your running for a head speed, if your head speed is to low your gyro is going to have a hard time doing it's job?
I tried to adjust the engine but I couldn't.
You have to get your motor tuned right, if your motor is not tuned right your gyro will never work right. Once you get your motor tuned right then you can find the gyro problem (if there is a gyro problem). A gyro will do all kinds of crazy stuff if your motor is not tuned right.
What servo are you using with your gyro? Pop the link off your tail servo and move the rod back and forth by hand, it should move nice and smooth (no tight spots).
You really should try and find someone that know about helis to have a look at it and help you set it up, it will save you a lot of time/money and headaches. It's no fun trying to fly a heli that is not setup right.