Seemed unhappy with a low-powered machine (5)
I believe the answer is:
moped
'machine' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for moped that I've seen before include "Was miserable; a vehicle" , "Light motor cycle" , "Sulked - form of transport" , "dejected" , "Light motorbike" .)