On the face of it, since Olaf's car already has an adequate electric pump, fuel vaporisation ought not to be the problem. But the symptoms definitely sound very similar to this.
I recommend that Olaf continues to pursue the blocked tank vent theory to conclusion. The tank is easy to access once the vertical fibreboard panel at the rear of the luggage boot is removed, just a few self tapping screws. Find the plastic vent pipes disappearing up towards the left hand rear qaurter panel and either remove them at the tank end and check that you can blow up through them, or if necessary cut them at a convenient point and rejoin with a short piece of metal tube after the blow through test. The parts diagrams can be found at
http://www.rover-classics.co.uk/images/reference/thumbnailv8/fuel/index.htm. I'm not sure which spec your car will be. There are two basic variants, one without any fuel spill return from the carburettors (ie any overflow goes to atmosphere in the engine bay) and one with a sealed system returning any overflow to the tank. The latter type is easy to spot because you have a thin "piggy back" tank mounted vertically behind the main tank, so that it is the first thing you see when accessing from the boot. If you have this system then there are an awful lot of breather pipes to block! If not the system is really very simple.
I can't remember whether the top of the breather pipes are to be seen inside the the base unit 1/4 panel - ie remove the padded finisher above the rear seats - or whether they are on the outside of the base unit underneath the bolt on external 1/4 panel. Either way to access you would start by removing the left hand seat base (pull firmly upwards at the front edge and then forwards) followed by removing the seat backrest (two self tapping screws at each side of the base of the backrest then push the backrest up). Then remove the soft trim panel to the 1/4 panel by tugging forward and out - it is secured on a lip and may well be fairly firmly glued as well. You can then see the base unit and if you need to go further then you can remove the external panel by undoing the obvious
4 screws that hold it onto the base unit. You would then be able to see both the inside and outside of the base unit in this area and the vent lines run vertically up to the roof level.
http://www.rover-classics.co.uk/ima...8/bodywork/gallery/pages/Rear Quarter_jpg.htm and
http://www.rover-classics.co.uk/images/reference/thumbnailv8/trim/pages/BC Post & Roof Trim_jpg.htm are helpful. You'll need some black silicon sealer to reassemble! Not a big job, perhaps 15 min to strip and 20 to reassemble?
Having proved your breather system then I think we are back to looking for issues giving a similar result to fuel starvation in the engine bay. Clearly things only go awry once everything is thoroughly warmed through, and return to normal after a bit of cooling. So I have a couple more suggestions. First make sure that your carburettors have the balck insulating block between them and the inlet manifold and are bolted up tight with paper gaskets at both joint faces for each carburettor - this to avoid heating the carburettor and to avoid drawing air into the maniflod after the carburettors. In a similar vein it might be worth renewing the valley gasket between the manifold and the heads. This is a rather larger job, but there are a number of different gasket types over the years, particularely for the later Range Rover engines, and if you have the wrong one it could displace the inlet manifold and allow it to draw air. Finally there has been an interesting post recently about coolant circulation within the inlet manifold -
http://www.p6roc.co.uk/Forum/phpbb3/viewtopic.php?f=5&t=5698 which is worth a read. If there were blockages within the manifold this could lead to overheating in the right area to cause your problems.
Hope this helps!
Chris
