I just finished fine tuning my Zero. Here is what I did and why.

Before test flying I have read, and heard from guys on the field, that the CG is wrong in the manual.

Move the CG to the wooden spar. I use an 8 cell KAN 1100mah so I had to cut out the foam to allow the pack to slide all the way forward so that it touches the cowling in order for the CG to be correct.

At that point it flew ok, but wanted to climb all of the time. Actually it flew great as far as handling goes. It does what you want.. except for the climbing part.

Next, since I am using a small brushless motor(Himax 2015-4100), I added 2 to 4 degrees of downthrust to try to correct this. No luck there. Flew slightly better but still wanted to climb all of the time. When I would do a dive it would pull itself out almost immediately. I was able to trim it to get it to fly correctly but then I was unable to fly inverted. If you are using the stock motor I would skip this step unless you later decide you need it.

I also tried changing the incidence of the main wing. I added 7/32" which translated to 4 degrees less on the angle of attack. This did absolutely nothing different.

After speaking to a couple more people on the field about their Zeros I decided to try one more thing. Adjust the elevator so that the bottom of the stabilizer and elevator are on the same plane. To do this I put the plane upside down and put a ruler on the stab/elev and adjusted it until they both touched the ruler flat. From the top of the plane this looks like down elevator.

This last step may seem rediculous but I saw a guy flying his this way and it was flying straight and level until he made it climb. I was about ready to retire the plane after 3 flights because I dont like flying a plane that I have to trim everytime I change the amount of throttle. When I set it up in this manner and launched it I was very pleased. Now it flies level no matter how much throttle I give it and responds correctly to up and down elevator. Also, flies great inverted.

Now its what it should be. Stable, good handling, and pretty quick. Of course the brushless helps on that last part.