snapping out of a loop means you have too much elevator, too far back of a CG, or both.

Now, depending on your engine and prop, you can improve the performance. A harder pulling engine will pull the plane through with out dropping airspeed on the up side of the loop. What engine/prop are you useing?

I usually set my elevator based on horizontal turns, going for as tight of a sustained turn as I can get. And I don't worry if that means that I might snap out at the top after a few loops as the plane drops airspeed.

Btw, always balance the plane level. The point it balances level is the current CG. Set that CG as per the directions, or as per your preferences. I personally like to move the CG back pretty far. This puts less load on the elevator, and actually results in a tighter turn. If you're holding the plane by the spot listed in the instructions, and the plane is nose-low, then you are some random distance too nose heavy. Figure out how nose heavy you are, and try moving the CG back.