That's a BIG Kara! So my results may not be the same as yours.
I have that same motor and use it on a modified version of the Hummer (mine is about 12.6' long and has a transom and is an all fiberglass version). It's a great motor for the boat. You won't win any races, but it'll move you along at a decent rate, even against a head wind. You don't want to get moving too fast anyway or you run the risk of driving the bow into waves. There are several stories floating around of Kara's or 4-Rivers boats becoming bass plugs when being towed.
Watch when you turn while under power as the boat isn't really built for cornering. It tends to just slide along the surface and the deck on the outside of the turn can dig in.
Scott