CIS Air metering unit - spring loaded case bolts
 

I am doing some maintenance on my 1980 Porsche 930 (3.3 Turbo), which is fitted with the original Bosch K-Jetronic fuel system (CIS).
The metering unit is the downdraft type, made up of two parts (upper and lower casing) which are screwed together with 15 m6 allen head bolts which are spring loaded.

I guess that this is to relieve pressure in case of blow-back.

The strange thing is that of the 15 bolts only 11 are spring loaded. The remaining 4 are tighten down.
Meaning that the blow-back will be limited or fail / damage the casing.
My first idea was that someone had messed this up in earlier times. But when I check the PET, it also show 15 bolts, 15 washers but only 11 springs, indicating a correct setup with only 11 of 15 spring loaded bolts.

Are they all supposed to be with a spring? If Not which are without springs and why?

What is the correct procedure for spring load? Tighten all inn and then one turn out?

I did a little searching, and while the NA CIS seems to have spring loaded at all mounts, the Turbo has a few that are not. Perhaps because it is a pressurized system?
Here is a Turbo set up for sale that shows both spring loaded and standard bolts used.
http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/1140769-930-air-flow-meter-complete-1978-1985-a.html
You might find more answers posting here. http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/

Thanks Ed... I checked with a Bosch shop in Germany, and.... it is supposed to be like this...But they could not give a good explanation on why.