[Paulporsche]

Dan, and possibly Stu,
Your cause may be a slightly too rich mixture. My engine was built and then installed by 2 extremely experienced pros, but I had some light throttle bucking. I cured it by nudging the mixture screw just a little bit leaner. This worked for years until my WUR finally went out of spec and had to be readjusted. I don't know if there was a relationship there because this was years ago and the whole CIS/control pressure thing was new to me. So I would check those pressures (Dan), check to make sure your sensor plate and plunger move freely, and check all ignition items.