It's actually a gas cutoff valve, not a switch. You push it in, and turn it upwards. This not only cuts off gas to the piston (thus disabling the action from being able to cycle in semiautomatic mode), but it also allows the firer to flip up the grenade sight.
If your asking about a Yugoslavian SKS 7.62 x 39, then these are some things to help identify one. All Yugo's have a grenade launcher on the end of the barrel just after the sight. They also have a blade-type bayonet unlike the Chinese which have a spike-type bayonet. Don't go by just the bayonet though because the Russian SKS has a blade-type bayonet also. Also, in between the sight and the gas tube on the top of the gun, they have a flip-up sight for the grenade-launcher. Hope this helps.
The Yugo version of the SKS MAY have a grenade launcher, and a gas shut off valve that is used when launching rifle grenades. That valve is well known to wear and erode, which results in some gas leaking when weapon is fired. If so, it may only cycle with "hotter" ammo. Try cleaning the weapon chamber thoroughly, ensure that the gas port is clear, weapon properly lubed- and visit website for suplusrifle.com for some info on dealing with the gas shut off valve.
1980s Yugo for sure.1980s Yugo for sure.
Yugo Nakamura was born in 1970.
Yugo-Zapadnaya was created in 1963.
Yugo Sako was born in 1928.
Yugo Sako died in 2012.
Yugo Serikawa died on October 4, 2000.
Yugo Ichiyanagi was born on 1985-04-02.
The cast of Yugo and Lala - 2012 includes: Lu Kui as Yugo Meng Quanlin as Bear
This is not the Yugo page, this is the Ford Escort page.
Yugo Saso was born on June 8, 1973, in Shiga, Japan.