John try 1/8 on both side. Some thing is going on with your plane because Zeros are great flying planes without bad habits , not like some plane such as sokhoi which the tip install was built into the design. Probably the guy before you who built the plane did not join the wings correctly. Get a Robart incident meter and check the wing incident and wash outs, also stand 6 or 7 feet behind the plane and check the horizontal stabilizer to make sure it is straight, otherwise your plan will like to rotate like a screw all the time.one more thing to remember is that the tail heavy planes like to tip stall. And finally as Falcon pointed out at low speed always use rudder to turn and ailerons only to keep the plane level. A bad habit picked up by all of us flying trainers is to use the aileron for everything. Please let us know what you found out. As the captain used to say "used planes are like a box of chocolate you never know what you get"