Shaggies diesel air bubbly problem - please help.

[shaggy]

Hi chaps. Ive got a real problem. The passat of doom is booked in to get its tracking and camber set up on Friday but Ive got a problem with air bubbles in the fuel line. I thought this was due to the veg oil heater that Id fitted. Ive by-passed that and returned it to standard IE: fuel comes into the standard filter then into the injector bump. As the engine is running in standard setup it missfires. If the engine is reved then a few seconds later air bubbles can be seen to be traveling down the fuel line and into the injector pump = missfire. All fuel line connections are tight. I have noticed that the fuel line that is daisy-chained from injector to injector and then back to the injector pump is a little worse for ware. Is this fuel line being air tight critical?? Im assuming that as you rev the engine the fuel will be taken from the most convenient source. Not sure where that is but if the daisy chained pipe from injector to injector is the most convenient then I guess this is where it'd be pulling air in. Is that correct?? Cheers Shaggy.