Dears,
I bought a Raptor 30V2 with a Thunder Tiger 39 engine, a Futaba gy240, and a Futaba 2.4 7CH radio. the plane flies good at first but suddenly it starts to turn left (nose left and tail right) by itself and I try to give it a full right rudder but it doesn't respond and keeps turning left until I reduce the throttle then it starts to turn right, also it really is hard to hover because of the engine, it keeps going up and down by itself so I can't keep the altitude steady, I need to know what is wrong with the engine and how to tune it.

I also need to know an approximate number of turns to adjust the low speed needle, I tried to adjust the engine but I couldn't.

A few questions to help pin down your problem.

I assume when you say it “turns” you are referring to the helicopter’s nose changing heading but the rest of the helicopter stays level. Depending on if you have heading hold turned on or not this may be normal, as long as it is a slow drifting motion and not a sudden spin. Vibration to the gyro can cause this effect to be magnified. The Gyro has 2 functions. In normal mode it is only used to stop the rotation. In heading hold the gyro will not only stop the rotation, but it will attempt to return the nose to the heading it was on before the drift or change occurred. A gyro can be fooled and this will cause gyro drift. In a hover, you will notice it a lot more than if you are in forward flight.

As for the engine. When you say it keeps going up and down, do you mean the RPM of the engine is rapidly changing up and down, like the engine is surging? Or do you mean when you start with a full tank the engine tends to speed up as you use fuel? As for a starting point for the low speed needle, that’s a hard one. Each engine is different. Your setting will change with humidity, temperature, and barometric pressure. Do you have a head speed governor set up. If so, the governor may not be set up properly.

I like to run my engine real rich. I get less power out of it, but it will make the engine last longer and I don’t do any 3D flying so I don’t need the power.

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, all I really need to know is this problem from the engine or from the gyro cause I bought the gyro used (Futaba gy240), and the heading hold is turned on and the gain is around 70.

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?

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.

Got any REVO turned on. That's a throttle to tail rotor mix. Could be setup in the wrong direction. Shouldn't even be active in HH mode.