Iv been having jamming issues with my V6 1.75mm and PLA (Colorfabb, Reprapper, faberdashery) also t-glase (i have not tried with ABS . been trying to find the issues and i belive its down to retraction. to test i tried pushing filament by hand down ptfe tubing untill i had a good flow. then retracted around 5 - 6mm when retracting i would get a jam and not be able to retract anymore. pushing filament quite hard would get flowing again. but any prints with lots of retraction are an issue with this. so i did test again and decided to remove PTFE tubing and this happens http://pic.twitter.com/Qamr5CGHWy every single time i do the test this happens. if you imagine a print that retracting a lot when retraction you would strip filament causing even more issues when trying to print. any ideas on a solution?