Classic mini MPI SPI flywheel Ignition ring

This video shows how to remove and check position of the reluctor ring fitted to the back of mpi and spi flywheels, SPI has 36 teeth minus 2 180 degrees apart and the MPI has 36 minus 5 (sometimes referred to as 36-4 . the timing can be advanced or retarded for turbo/ supercharger or to suit different fuels.
Some clutches can change the orientation of the trigger points this will stop the car starting.