Here's 2 ideas:

 

1) Build proper race areas for these bikes to go to. Ensure the kids have safety gear and charge them a fee to race. make some money.

 

2) Close down the shops that sell these parts which are making the bikes illegal. My guess is a lot of the kids buy stuff as opposed to making it themselves.

This seems to be a weekly activity - perhaps the penalty is not severe enough, perhaps the bikes should be permanently impounded and sold with the money going to the a fund so police could receive a 'livable wage'.

i agree with all comments .crush the said bikes .that will slow down the offenders   !!!!