A crackdown on dangerous or antisocial moped or scooter riding in Bristol has seen 17 machines taken off the road for defects or illegal modifications.
Five riders were issued with fixed-penalty notices for not displaying L plates.
A police spokesman said nuisance bikes were one of the most common complaints the force received.
"The way bikes were altered to boost speed or make their engines louder invalidates any insurance," he added.
The parents of riders who had their bikes confiscated were required to collect their sons or daughter's machines from police.
"The feedback from parents was very positive: a lot were just unaware of how these bikes had been modified or the poor mechanical state they were in," Sergeant Tim Chandler said.