It's easy removing carbon - just a small amount (4)
I believe the answer is:
inch
'small amount' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for inch that I've seen before include "nose" , "Move in tiny increments" , "Edge along" , "A very little" , "... or not so long < , Celtic island" .)