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So, just tweeting things (998 Cooper) and I notice that when I apply vacuum the baseplate in the dizzy is very jerky… also as the vac comes on the baseplate moves up to say 12 o’clock slightly before it starts to turn… is this normal??

Kevin

No, it's not normal. You should first remove the vacuum unit and bench test it away from the distributor, to eliminate the possibility of it being a stiff /stretched diaphragm. then you can access the baseplate to see how well the baseplate pivots independent of the diaphragm. Both should be smooth in operation.
Lube the baseplate pivot while your in there.

Hi, thanks. I’m applying a vacuum to the dizzy without the vac unit in place.. sounds like I need to get the plate out and take a look…

From memory, there's a spring thing fixed to one of the plates that keeps the two plates apart. (It might act as an earthing strap between the two plates too.....). On my old Cooper, this spring thing chafed into the other plate and made the movement between the two plates very bitty and notchy just like you describe. I had to polish the area out with a bit of emery and it cured it

Thanks Peter, will report back when I’ve had a good look…

Kevin