Hi Hoff, thanks for your reply.
Well, I spent the better part of the morning driving miles to collect a second hand vac resorvoir from a vw scrapper and then hunting down vacuum hose as the three automotive stores I went to don't stock it any more. In the end, some 6 mm was sourced from a hose supplier on an industrial estate. He didnt have 5 mm. But what difference will a mm make? Its not like we're talking engine internals?
Well it made plenty of difference in the sense that a couple of the connections were too sloppy and just not fit for purpose. So, will just order some more online. The vac resorvoir went on a treat and crossing my toes while connecting the new hose to the fragile nipple did the trick.
Took it for a nice long drive afterwards and there is very little smoke coming from the exhaust now but the performance is the same. Accelerates smooth and fast down hill, can get up to 70 mph on flat stretch of motorway but going up any sort of moderate incline she just falls flat on her butt!
So, tomorrow morning am going to remove the bumper and clean/replace the MAP sensor to see if that might be the culprit. Failing that will look at replacing the n75 valve and after that cross more body parts. Lol