Hi and ditto on the welcome. My guess too would be in looking at the valves. Pull the valve cover and see if the exhaust valves are opening. An exhaust valve not opening would cause the burnt gases to exit through the intake and carb. It would be accentuated at higher rpms because you're sending more gas into the cylinder. Could be caused by a bad lifter, bent or broken pushrod or burned valve. Let us all know what you find.
