Mk1 Golf 1.6D Air leak issue

[AZIM]

Im no a diesel expert so you can say im a newbie to diesels
Got a mk1 diesel 1.6 golf ex van which has air leak problem .
Id say its not tank related but more from forward of the fuel filter side .
The reason is that when i start her up she splutters and does not run smooth .
When i stop cranking i can see pockets of air bubbles traveling rearwards in the clear fuel line ,between
the injector pump and the fuel filter .
The pump is not showing any leaks and niether are the lines or injectors .
How do i go determining where the air leak actually is .

PS the car had been not running for about 10 yrs when i got hold of her 

[Doug]

Assuming that you have replaced the fuel filter, then look at the water fuel separator. These plastic boxes age crack then are a common source of air in the fuel or even losing prime. Just bypass it with some neoprene fuel line and a few clamps. Use vise grips to clamp the flex lines on either side while you fit in the bypass piece. That way you will not lose the prime on the system from the tank to the pump. It will put an end to much frustration.

[AZIM]

Thanks Doug ,will look at those things you mentioned .
I have not replaced the fuel filter but merely removed it inspected the seal ,
primed it with fresh diesel and refitted ( i will now replace this ).
Where is the seperator you mensioned ?.

[Doug]

The separator is located just forward of the fuel tank on the underside of the cabin. You can't miss it if you trace the supply fuel line back from the filter. Definitely change the filter first before doing anything else. Give the engine a good workout to see if that this is the problem area. If it is a 10 year old filter it is a trouble maker.