[MP2]

Okay, it's quite simple. No timers needed. When they enter a checkpoint, use GetVehicleHealth and check if it's lower than x (I would recommend 500 health).
If it is, SetVehiclePos back to the start, and show the first CP again.
Simples.

Also remember to fail them if they die.

Oh and, you should set curCP to 0 when a player starts the race, to ensure it doesn't break.