Specna arms M4 trigger issue

[Wegalaxy]

Hello,

I have a Specna arms m4 with a trigger issue.

When I put the rifle into semi auto and pull the trigger all the way it works.

But when i pull the trigger lightly it bursts into full auto.

I am feeling confident to fix it my self.

Does anyone know what the cause of this problem is just so I have a rough Idea before i open the gear box up.

Thanks 

[ButcherBill]

You might not need to open the gearbox, might be something simply external of the gearbox but hidden within the receiver.

[Wegalaxy]

@ButcherBillis it that little spring that is exposed?