[blykins]

One thing could be the state of tune. If a carb has a lean spot right off idle, it could cause a hesitation or buck.

Most likely, what you're experiencing are the characteristics of the cam. A lot of engines have a personality more for upper rpm running and they're very inefficient at low rpms. If you happen to be driving/cruising in that rpm range, you can get the "buck".

With the engines that we do, sometimes you can get away from it, sometimes you can't. But usually, we try to make sure the transmission is such that when you're cruising, the overdrive ratio allows the engine to run at an rpm where it's out of the buck zone.