Hi, Dennis - the K&B weighs 6.9 ounces, the B-15 with muffler weighs 5.6. Notice that I moved it forward around 5/8 inch to compensate.
It also used around half the fuel that the K&B used - Brodak 10/23.
I'm really impressed with this little engine.
A small stunt ship is in the planning stage.
Bob Z.