Enough is enough...!

Ok, so I've got a 1989 Clipper Cabriolet.

The car has been running poorly of late, mainly when warm.
I have a Weber carb(new) and the engine runs very smooth on idle. Once warm and when driven, the car drops revs on load and wants to cut out.
I have/had a vapour separator(brand new) connected. Once I removed this the car ran very well for around 3 weeks. In this time I did 20 mile journeys and the car was fantastic.

Tonight I took the car on the motorway and after about 4 or 5 miles the power started dropping until I eventually dropped speed so much I had to pull over.
I checked the inline fuel filter (before the fuel pump) at this point and it was pretty much empty.
I turned the engine off and the fuel filter filled up again.
I drove another mile before the power dropped off again.

What I've replaced:
Fuel Pump
Carburetor
Fuel vapour separator
Fuel tank sender
Coil
Distributor cap
Rotor Arm
Spark Plugs

In between the car running well and my journey tonight I have added 1/2 tank of fuel. Weather-wise, there has been a fair bit of rain (relevant?)

Also, despite the car running well, it had needed a bit of accelerator to get it started on a semi-warm engine. On a warm engine it would start very quickly on a key turn.

Help me out…I'm running out of ideas and want to get my car running well again!

Have you had a look at the fuel filler neck, shine a torch down it and look for any holes as water and dirt in petrol don't mix well.
There sometimes seem to be a problem with Webber carbs as they need to have a restriced fuel return pipe, a welding tip seems to work for some people.
Try removing the fuel return pipe from the carb and blocking it off, if the car runs better then restrict the fuel return, you do need to have a fuel return or the carb will get flooded.

Try googling this problem and you will see lots of posts about it.

Thanks mark.

The fuel filler neck is also pretty new and has no holes.

I'll take a look at the fuel return from the carb.

Just another thought… Have you looked at the rubber flange which the carb sits on? with the car ticking over try wobbling the carb and if the engine tickover changes you may have an air leak, the rubber goes hard and splits over time.
https://www.vwheritage.com/shop/026129761A/carb-flange-mk1-2-golf-scircocco-fitted-with-a-pierburg-2e/?gclid=COGokN2wvsUCFYnLtAodiigAxA&country=GB&lang=EN
 

Thanks again mark.

The rubber carb flange has also been changed so I can rule this out.

Rust/rubbish in the fuel tank,???   gradually blocking the outlet, once you stop the petrol seeps back and its ok for a while. but ive never had a soft top so don't really know the fuel system.

sounds liek carb icing to me, have a read thru:
http://www.clubgti.com/showthread.php?144497