CA mp5 fire selector problem

[airsoft_ben_1989]

Right, I have a CA mp5 b&t and when i select single shot, more often than not it fires full auto.

how do i stop this????

would fitting a mosfet stop it or not? as i quite fancy having a 3 round burst when set on full auto then holding the trigger for full auto. i intend on using single shot quite a bit which is why id rather fix it than live with it and just feather the trigger.

Thanks