What causes exhaust pipe turn red on a motorcycle?

In a 4 stroke and 2 stroke bike there is things that can cause that:

1º-Valve is of the compression timing. ( 4 Stroke Bikes Only )

2º-Ignition Stator out of timing.

3º-Filter or Carburetor letting to much air inside, causing a furnace affect because the amount of gas and air is not even!