Busy when fuel escapes freely out of a hole (8)
I believe the answer is:
eventful
'busy' is the definition.
('eventful' can be similar in meaning to 'busy')
'when fuel escapes freely out of a hole' is the wordplay.
'when' becomes 'e' (I've seen this in other clues).
'fuel escapes freely' becomes 'ful' (I can't explain this - if you can you should believe this answer much more).
'out of' means one lot of letters goes inside another.
'a hole' becomes 'vent' (vent is a kind of hole).
'e'+'ful'='eful'
'eful' placed around 'vent' is 'EVENTFUL'.
Can you help me to learn more?
(Other definitions for eventful that I've seen before include "Action-packed" , "Lively and exciting" , "Notable, full of incidents" , "Packed with action, lots happening" , "Consequential" .)