Questions about fuel pump

[fafou]

Hi,

sorry in advance for this newbie questions but I really can't figure out how the pump works ?
I hear it during five seconds each time I turn the key on and then it stops. Since the motor isn't running, the gas can't go to the carburetors (depression valve), so why running the pump before startup ?
Also, what is the purpose of the fuel switch ? Does it turns the pump on when running ?

Thanks

[DonTZ125]

The pump runs at the start to make sure the carbs are properly filled up. That switch is your Reserve switch; when the fuel level sensor drops to a certain point, the TCI either cuts spark to one bank of plugs (1-4 or 2-3) OR it turns the pump off, causing the carbs to empty and the engine to sputter - I forget which on your model. Either way, this is your signal that you're running low on fuel. When you flip the switch, the pump / spark returns to normal operation.

[fafou]

ok thank you for the answer.
On my model it must be the cutting of the pump because I already ran few miles with the fuel level light on and without the switch on "res" without noticing any sign of loss of power (the fuel level was certainly still enough high to feed the carbs).

So if I understand correctly, the pump operates in permanence when the engine is running (with full tank) ?

[DonTZ125]

Correct. The pump also has an internal pressure switch, so that when the carbs are full and the float valves are closed the pump shuts off.

[fafou]

ok, I was also worried about that because I didn't see any return line to the fuel tank.

Thank you ! Now I know my bike a little bit more !