OT..351C vacumn question?

351c, 2v. The vacumn advance runs off a tree valve (don't know the real name for it) on the thermostat housing. There is no, or little vacumn at idle but on acceleration vacumn rises. The car has a stumble just off idle, you know the one, where you break your nose on the steering wheel and then get whip lash when it catches. It appears that there is instant vacumn on acceleration, but if it is not here at idle could this be the cause of the stumble? TIA, Tbolt