UPDATE: It looks like the snap problem is due to too much left engine thrust. In straight up vertical climbs, it would go left. Rudder trim was required to make it climb straight, then loops after that were MUCH better. I've got the engine mounted with hard rubber faucet washers between the mount and the firewall, so I'm going to try turning the right screws in one turn, and the left screws out one turn, and see what that does. Otherwise, I'll just add a metal washer on the left side. Also, I was going the wrong way by adding weight. I'm down to 2 oz's now, and it is flying better. I bought this plane used, and don't know exactly what the recommended CG point is, so I guessed. I forgot that swept wing planes usually have a CG point a little farther back. Once I get the CG and the left thrust correct, I'm going to dial in the up/down thrust.
I'll keep ya posted!