found a pair of 40 IDFs at a wreckers today and picked them up for a criminally low price. someone had hidden them in the back of fasty, I guess to
come back and get them, but oh well, you snooze you loose eh! 
Anyway, they seem to be off a late alfa 33. The last boxer they released during the 80s. They are complete and in reasonable nic although some of the
adjustments on the bottom of the carb seem a little different from some pics of IDFs I looked at on the web.
VS this...
The air bypass and the idle mixture adjustments seem to be sealed off. I guess that's normal for a factory setup.
Are they any good for a VW? or should I put em on ebay?
I think they'll be fine as long as you can make the idle mixture adjustment functional, probably just involve drilling and tapping the hole for a
mixture screw.
I'm currently running 36idf's on a stock 1600 and their essentally the same as my 44idf's, except for a few minor differences on the idle circuit.
By the way, are you sure there 40's?
They really look like 36's.
x2
im pretty sure alfa 33s had 36IDFs
but still a good carb for a mild bug motor if u get linkages and manifolds
The only other drama you will normally have with these carbies is that they are not left and right handed so you will end up with one with the linkages against the firewall which is a right pain in the bum as trying to weld on a linkage on the other side of the carby is agin a pain and seldom works well , so sorry to say Pete but they may not be the bargin first thought , not to mention as noted above they are more than likely only 36's
By the time you buy manifolds, linkages, jets to suit, aircleaners with tops and bottoms, and modify for idle mixture screws and air bypass, you may
as well buy a new set of Kadrons! (which will outperform the 36's)
Put them on ebay.
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they are definitely 36s. I measured then with my calipers last night. The calipers I used before were someone elses and I wasn't used to them. They
are a match pair too. I only paid $100 for them so I don't think I've lost anything. Surely a matched pair of italian webers is worth that. I've
got a few mates with a 1600s who might like them anyway so I haven't lost anything. Failing that, I can always use them for a hot 1300 in years to
come. 
You will need new E tubes as Alfas had F57's.
They do not work - trust me.
Hopefully the good news is they come stock with 32 vents - good for 1600's
Your idles are in the top. Better access than the pic of 40's on the side
The bypass is soldered up.
Have heard 2 stories about if this is good or bad.
You also need to modify the joint where the hex bar connects, as you cant connect onto the ball joint as shown
are there any good sites that can show me what's what on them?
pete,
try: http://www.carburetorclinic.com/36_idf.htm
shows exactly whats needed.
$100 is good - will work on bigger than 1600s too - just depends on what you want out of them.
ta, great page there.
I think I'm missing a few screws, but aside of that they seem to be complete. I guess they'll go on a street or dirt khana style 1600. Something
where torque is more important than a 9k redline anyway. 
They are universal webers, not a left and right side only setup because you have idle adjustment screw threads on both sides of carb, my first 40 idf webers were one side only was a PITA but i made a custom linkage and they worked fine.