Knock up a stink over fuel (8)
I believe the answer is:
paraffin
'fuel' is the definition.
(paraffin is a kind of fuel)
'knock up a stink over' is the wordplay.
'knock up' becomes 'para' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a stink' becomes 'niff' (niff is a kind of stink).
'over' is a reversal indicator.
'niff' back-to-front is 'ffin'.
'para'+'ffin'='PARAFFIN'
Can you help me to learn more?
(Other definitions for paraffin that I've seen before include "Liquid fuel" , "Kerosine" , "Petroleum product" , "Kerosene" , "Possibly oil" .)