It's good when you talk (3)
I believe the answer is:
'you talk' is the definition.
'gas' can be an answer for 'talk' (gas can mean to chat). I'm not certain of the 'you' bit.
'it's good when' is the wordplay.
'it's good' becomes 'g' (abbreviation).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
Can you help me to learn more?
(Other definitions for gas that I've seen before include "Possibly noble" , "Chatter vapidly" , "idle chit-chat" , "Hydrogen or methane, say" , "Hydrogen, for example" .)