Don't use your even feed foot (walking foot), switch to your darning foot (hopping foot). Drop the feed dogs on your machine and practice, practice, practice.... it takes a bit to get your timing right between your foot control and moving the fabric to keep your stitches even.... you will find if you go faster it is easier to keep the flow.
I free motion all the time and I have never touched my tension, once I found my groove it just flowed and my stitches were even. Oh, almost forgot... practice, practice, practice.... and most important of all..... Have Fun! :)