What is the purpose of checking the ignition timing of a motorcycle engine using a timing light, and which flywheel marks are referenced?

1. To verify that the spark occurs at the correct degree before Top Dead Center (TDC) by aligning the 'F' (Fire) mark on the flywheel with the crankcase index mark.
2. To check if the starter motor is spinning at the correct speed using the 'S' (Start) mark.
3. To align the transmission gear shifter using the 'T' (Transmission) mark.
4. To measure the crankshaft end play clearance using the 'T' (Tension) mark.