I just wanted to pass along how easy it is to decarbon your pistons using Berryman Chem Dip. I'm sure many of you know about this product. It comes in a gallon paint can and has a dip tray inside, for about $30.
Just soak for 15 - 20 hours and scrub pistons with a stiff nylon brush and some Simple Green. If some remains resoak overnight or longer. Chem Dip rinses off well with water.
Sometimes the ring grooves need a second soak or the piston head but this dip takes off any and all carbon or buildup with little work.