Sulked on a motorbike (5)
I believe the answer is:
moped
This clue is a double definition.
'sulked' is the first definition.
(I've seen this before)
'motorbike' is the second definition.
(I know that moped is a type of motorbike)
'on a' acts as a link.
(Other definitions for moped that I've seen before include "Two-wheeled vehicle" , "sort of bike" , "Vehicle - was blue" , "Two-wheeled transport -- was in low spirits" , "Motor cycle -- sulked" .)