Clean up a chap's vehicles (6)
I believe the answer is:
mopeds
'vehicles' is the definition.
(moped is a kind of vehicle)
'clean up a chap's' is the wordplay.
'clean up' becomes 'mop' (I've seen this in another clue).
'a chap's' becomes 'Eds' (short for Edward).
'mop'+'eds'='MOPEDS'
(Other definitions for mopeds that I've seen before include "Lightweight motorcycles" , "Low-powered motorbike" , "Light motor cycles" , "Low-powered motorbikes" , "bikes" .)