Carelessly rated large European lever (7)
I believe the answer is:
treadle
'lever' is the definition.
(treadle is a kind of lever)
'carelessly rated large european' is the wordplay.
'carelessly' is an anagram indicator.
'large' becomes 'L' (eg in clothes sizes).
'european' becomes 'E' (abbreviation e.g. EU).
'rated' is an anagram of 'tread'.
'tread'+'l'+'e'='TREADLE'
(Other definitions for treadle that I've seen before include "Rocker in a factory" , "(Machine's) foot-control" , "Foot lever giving power" , "Machine foot-lever" , "operate a spinning-wheel" .)