Aileron Balancing is well covered in the manual, but since it's so critical I'm going to include it here so folks have quick access to it (parts are in several sections of the manual. There are a couple of critical measurements to avoid aileron flutter.
NOTE: This is in no way a substitute for the builder's manual! Always build your aircraft per the manual.
1) Ailerons should weigh about 9 pounds, but must weigh less than 9.5 pounds
2) When hanging from the hinge line upside down, the top surface (bottom when hanging) must be level or slightly nose low
(leading edge lower than trailing edge). Place a torpedo level. Add weights as needed to meet this requirement.
3) You must have at least 1/16" clearance all around for wing flex, especially in front of the counterweights, and 2 1/2" deflection up and down at inboard trailing edge
Overall balancing process
Aileron Travel Requirements
Wing control tube connections