Yamaha DT125E 1977 Owner's Manual page 10

Fuel petcock
The fuel petcock supplys fuel from the tank
to the carburetor while filtering the fuel.
The fuel petcock has three positions:
OFF: With the lever in this position fuel will
not flow. Always return the lever to
this position when the engine is not
running.
ON: With the lever in this position fuel
flows to the carburetor. Normal riding
is done with the lever in this position.
RES: This indicates "RESERVE". If you run
out of fuel while riding, move the lever
to this position. THEN, FILL THE
TANK AT THE FIRST OPPORTU-
NITY.
Starter knob
When cold, the engine requires a richer fuel
mixture for starting. A separate starter circuit,
which is controlled by the starter knob, sup-
plies this mixture.
Pull the knob out to open the circuit for
starting. When the engine has warmed up push
the knob in to close the circuit.
1. Starter knob