Now to install the distros into a USB drive, you need to format it clean. What these utilities like YUMI and Unetbootin does is just copy files over and make them bootable.
Some large USB sticks are partitioned thanks to previous distro installs. So you have to repartition it. It is troublesome. So we got RMPREPUSB.
http://www.rmprepusb.com/
install this program.
For distro on a stick, make sure the USB stick is set to non-bootable and FAT32. Then prepare drive. As simple as that. It will close all windows since it is a DOS operation.
It will partition it entirely to one partition and format. Quick and easy.