Can't seem to run 2133mhz memory on my FX6350 build


So I bought a new kit of G.Skill Ripjaws X ram (2x4gb) and it's rated to run at 2133mhz Cl9. But I can't run it at the advertised speed, the best I can do is 1866mhz CL9. Any suggestions of getting the ram to it's rated speed?

Mobo: Ga78lmt-usb3 rev 6.0

CPU : FX 6350 at 4.2ghz

RAM: RipjawsX - F3-17000CL9D-8GBXM - G.SKILL DDR3 Memory