prusa i3 irregular flow rate

hi everyone from italy, that's my first post.
i have a DIY prusa i3 (i think is a rework) with a 3mm e3d v6 hotend (bought the kit here http://www.emakershop.com/browse/listing?l=1126 )
although i struggled a bit setting up everything it worked for a while nicely, i used a couple of spools of pla and also one of abs.
since the beginning of august i'm having a lot of issues, the flow from the nozzle is becoming very variable, sometimes it even stops. Seems like the filamet gets stuck somewhere, the extruder motor is working but the hubbed bolt digs into the filament. if i pull out the filament and then reinserct it works for a while.
this is how prnits look like http://forums.reprap.org/file.php?35...928-WA0012.jpg

I've tried to change almost everything, the whole hotend, tried a couple of cold ends both in pla and in abs, i bought a new hobbed bolt and tired serveral tighening torques, changed the spool position but still i can't solve my problems..
do you have any idea of what i'm doing wrong?
thank you

here is my marlin firmware http://forums.reprap.org/file.php?35...zip,download=1

i'm printing pla and i've tried several temperatures in the range 190°C-205°C for the extruder, 75° C for the heated bed

Sounds like a basic clogged nozzle, but you say you replaced it with the hot end?

I replaced the whole hot end. Seems like the filament gets stuck in the very first mm of the hotend

Then that sounds like a mis-aligned part in the hotend. Maybe the nozzle is not seated properly.