mobile

I have LG p769 from T-Mobile (rooted) running stock android 4.1.2. I want to try cyanogenmod on my phone, and see how well it does. I have alredy backed up app data and system data using Titanium backup. Now I want to backup the stock ROM in case if anything goes wrong. I tried using ROM Manager and TWRP Manager but neither of those support my device. I've searched all over the web and couldn't fing anything. I seriously don't know why there is no way to backup the stock ROM for p769. Can someone please help me through this? Thank you.