I'm new when it comes to gas engines. I have a Zenoah G-23 on my 1/4 scale Sig extra 300xs. I watched the identical set-up at an air show and it flew great. Mine is diving to the left as soon as it gets off the ground and I have to keep using right aileron to straighten it out. It's a real bear to try to fly. I'm lucky I havent crashed it yet. I have re-checked the side to side ballance and it's perfect. I have the back plate of the engine mounted to the firewall with a piece of 1/8 " thick rubber between for vibration. Is this engine thrust doing this? Should I add some washers behind the left side of the motor mount? I'm afraid to take it up again without figuring something out. Thanks for the help!

Does it still turn left when you throttle back? If so you may have a warped wing. If not add washers to the left side about 1/8 in. at a time till it straightens out.

I have that same plane with an FPE 2.4. I'm sure you know from reading the manual that the fire wall is at zero degrees. I agree with Flypaper except for the 1/8(.125) I think thats alot. My 2.4 has a center to center hole pattern of 3 inches across the top, I'm going to put in 1 1/2 degrees of right thrust. That's .078 thick washer, a little more than half of that 1/8. But even at zero thrust my plane is'nt doing what yours is.