It is probably a typo and they should have wrote exhaust valve. It's thick enough to be an exhaust valve. The cylinder head has both an intake valve and exhaus

It is probably a typo and they should have wrote exhaust valve. It's thick enough to be an exhaust valve. The cylinder head has both an intake valve and exhaust valve on each cylinder. One to let in misted fuel and air (delivered via the intake manifold, which is via fuel injection rail or carburetor jets), and another to allow the dispelling of combusted fuel. That said I've seen carbon build up on intake valves too. Usually from bad valve adjustments or improper seating...bad lifters/rockers etc etc so they port isn't properly sealed in combustion. Nothing to do with being fuel injected or carbureted. It all comes via the intake manifold... The valves know absolutely no difference.