My 4* 40 didn't straighten up and fly really right until I installed some right thrust AND some down thrust at the same time. It grooves perfectly now. Nicest plane I have ever flown.

Also, is the wing sitting perfectly parallel to the stab on the fuselage? Sometimes ailerons will have a bit of a warp in them, and it is a matter of continuing to adjust the linkages until she flies straight.

Ernie