Hi Gunther,
13 mpg is a rough estimate - I kept track of my fuel consumption and mileage this summer after having fixed my speedometer last spring. I'll calculate my real mpg soon. I usually go out for short rides where there is a lot of acceleration/deceleration so my mileage suffers. The noise it makes is addictive! It's another good reason to get those carbs tuned though; fuel economy and less emissions.
Here are some links; there are many more I'm sure:
Scroll down this one and look for A Quiet Boom's comments. He describes full disassembly/assembly/set-up procedures:
http://forums.pelicanparts.com/porsche-911-technical-forum/311856-zeniths-stock-2-7l.html
Thread by 1QuickS:
http://forums.pelicanparts.com/porsche-911-technical-forum/566366-zenith-40tin-service-design-review.html
Hers'a another good one:
http://forums.pelicanparts.com/porsche-911-technical-forum/797607-zenith-rebuild-my-first-carby-project.html
And finally the ultimate reference (I printed this one and put it in its own binder):
Zenith 40 TIN Carburettor Manual
You're in Ottawa and have Zeniths? We should get together next summer and compare notes. Porsche guys regularly get together on Sunday mornings for coffee. Here's the only time I could attend, the meeting being held at Landsdowne:
http://forums.pelicanparts.com/canada/619335-ottawa-cars-coffee-37.html#post8812892
Michel