As the carburetors are basically unserviced since day one I expected a problem here, so I checked the left carb first...
... and I found this: a brass tube on the ground of the housing!?
... which belongs in the cover:
so I refitted it into the cover:
and while I was at it, I cleaned the float bowl housing from some dirt and slime:
then I assembled everything again. When I thought I was ready I checked the engine bay - just to spot this one:
... I forgot to install one of the carburetor gaskets - so, all steps in reverse order...
I also spotted a fair bit of oil below the breather tube:
So I replaced the paper seal with a composite one, I hope it will stop spilling oil now...
P.S.: unfortunately it didn't run better afterwards - I will check for other issues tomorrow!
The spark plugs are all tan-colored and the distributor is in perfect working order, also the ignition timing is o.k. - mmmmh?