Hi,
My crankcase halves (not the side covers, they are ok) have only got about 50% of the black paint on them since I scrubbed them clean.
So, I’m in need of a rattle can to make them look more presentable. I presume no primer was used on these, so it will be a spray that is suitable to go straight on to aluminium?
is the original finish satin or gloss black?
I assume the carburettor will need the same spray when I get round to it.
Thanks…..

Are you sure some of the covers don't have a "magnesium" marking?  For the ones that do, special prep is required or paint won't stick very well. 

Special (expensive) primer for magnesium works or as strange as it sounds, wiping it down with Gibbs Brand Lubricant works.  (this is a special product, you must use Gibbs Brand.)

Half asleep.  I just noticed you said center cases. 

I'm not the guy to ask about paint but I remember cases being more of a semi-gloss and the carb being very glossy.