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Discussion Starter #1 (Edited)
Hi all

I am new to this forum so I hope I am not going over old ground here. I would like help to really understand the operation of IDF fitted to many Alfas, Porsches, VWs and other applications so that others do not have the problems I have had getting these carbs working. In fact I think that a lot of the complaints that people have about Weber IDFs are really down to a misunderstanding of how they work and the criticical settings of things such as float level.

Also it seems that there can be considerable differences between these carbs so that certain information can in some ways be misleading because it does not apply to specific formats. For example I have a pair of Weber 40 IDF 82/83 that unknown to me had idle screws with a 0.5 thread pitch (ultra fine?) rather than 0.8 (fine?). This meant that when turning out the idle screws, I thought that the number of turns out was way to much for the taper to be effective. I had almost abandoned the carbs as faulty till I discovered the difference.

I think I have a pretty fair understanding of these carbs but there are still many things that I think we can collaborate on to increase our understanding of the IDF family, their differences and applications. If anyone is interested please let me know and we can work out what format to use.

I know that there is a lot of information/books out there about these but these are not in a single place, freely available to all or properly peer reviewed, and I think it that others would benefit from the struggle that many of us have had with understanding IDFs, which in the end turn out to be first class metering devices.
 
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Good luck in your quest. You don't say which engine you want the carbs for. Are you looking for jetting and choke information?

I have recently bought three Weber DCNF carbs with a view to using them on a 24V 2.5 V6, although they are 40 DCNF and may be a bit on the small side. I don't have an engine for them yet either! For me it's very early days and I'm just investigating the idea as a possibility for my kit car.
 

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Discussion Starter #4
hi mudhut. thanks for the reply. i don't really know very much about DCNF but they look similar to IDF's, are they a good alternative? i am not really looking at the carbs for any particular application, its just that there seems to be a lot of missing information, misinformation and half truths out there.
 
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It's certainly true that collecting the data all together in one place has sort of been done in various books but the one I have (How to Build and Power Tune Weber and Dellorto Carburettors) focuses on some models better than others and there are some gaps in the info too.

The DCNF thing is because they are more compact than the IDF and there's not much space in the V of the 24 valve Alfa engine. I understand from somewhere that they may not be quite as good as the IDA or IDF. Don't know much about them as I've only ever had Dellorto DHLA before on another car.

As you say, there do seem to be myths and half truths around. Basic venturi sizes and main jets seems to be fairly well served but the finer points of progression holes, emulsion tubes, accelerator pumps and setting up/diagnosis seems not so clear.

Are you after basic jet stuff for engine size and rpm or are you trying to make something of a master table of as much reliable info of any type as you can find? The latter I suspect. Could start by collating existing info in books like the one above and also from other places like Guy Croft, The Fiat Page, specialist forums for Lambos, Lancias, Ferraris, Porsche, VW.

Going to be a big job and after that I suppose there's no substitute for hands-on experience. I'm no expert by any manner of means though I'd be happier with SU carburettors. Only done a little with the DHLAs (which I really quite like even though I've not had the chance to compare with equivalent Weber or Solex types.
 
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