OK so that’s confirmed then. NinjaFlex wont work with my bowden and extruder 
Common airtripper problem. Try opening up the filament entry hole to 4mm and insert a short length of Bowden tube that can butt up against the hobbed pulley. Should prevent most buckling issues.
@Tim_Rastall Are you saying printing ninja flex with a bowden is more possible than most seem to think? Is that what your kraken has been up to with that bowden? Confident enough to say it’s workable?
@Anthony_White by no means, I’ve not had a chance to play with Ninja and I imagine printing performance decreases significantly with the length of the bowden tube being used. The fix i mentioned just solves the design flaw in the airtripper.
The extruder works best with grooved drive gears that keep the filament in line with the idler bearing. The distance between the idler and the in-feed was to allow different size drive gears.