http://appsandtips.blogspot.com/2014/11/how-to-rootrecovery-lg-su640-jellybean.html

How to Root/Recovery Lg su640 Jellybean (4.1.2 30d/c)

1. ROOT
Update TNT new Root 
https://docs.google.com/file/d/0BwuJnNfF1xTnb21pR1Z6NDNyeXc/edit?usp=sharing 

*download file and extract it
*Enable USB debugging 
*connect with pc select lg software mode
*open TNT_LG_JB_Root.exe
*press any key
 remove usb
 disable usb debugging
 Re-enable usb debugging
 connect usb
 press any key

I wish you success! 
 
2. CWM: 
Download the following file to decompress connect usb debuging mode + LG software 
Click on Flash.bat
Accept su acess from phone !
http://www.mediafire.com/download/1j9zcbkahhakrb5/cwm_su_640.rar