Go on too long about career (7)
I believe the answer is:
overrun
'go on too long' is the definition.
(I've seen this before)
'about career' is the wordplay.
'about' becomes 'over' (both can mean around).
'career' becomes 'run' (career can mean to run or move out of control).
'over'+'run'='OVERRUN'
(Other definitions for overrun that I've seen before include "Move too fast" , "Exceed (allowed cost/time)" , "Flood" , "Swamp (an area)" , "Plagued by" .)