IDF dimensions

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ward00
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IDF dimensions

Post by ward00 » Thu Sep 05, 2019 10:25 pm

I am trying to figure out what the designation for the 40 and 44 IDF carburators means. If it is a dimension, can't quite find one on the carburators that correlates to the numbers.
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Special
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Re: IDF dimensions

Post by Special » Fri Sep 06, 2019 1:11 am

40 or 44 is the diameter of the barrels

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davedecker4
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Re: IDF dimensions

Post by davedecker4 » Fri Sep 06, 2019 3:03 am

It should be printed or stamped on it somewhere.

Also the chokes go in the top and reduce this. That may throw you off a little.
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bartigue
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Re: IDF dimensions

Post by bartigue » Fri Sep 06, 2019 5:25 am

All carburetors have a barrel size (40, 44 in this case) and venturis within the barrel to reduce the size. This reduction causes an increase in air velocity. Velocity needs to remain high, especially at low speeds, or the atomization of fuel will be poor.
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ward00
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Re: IDF dimensions

Post by ward00 » Fri Sep 06, 2019 1:06 pm

Its obvious that the dimensions are different between the two carbs, I was just wondering do the numbers correspond to a measurement that is taken at a particular location, or are they just an approximation. On my carbs, I cant seem to find an exact 40mm or 44mm dimension - perhaps because they are not original Webers?
Currently in Santa Cruz, Ca
75 Spider - 1.8 with IDFs running like a champ - starting performance race upgrade to 2 liter
75 Sport Coupe restoration

Past
Spider (4), Coupe (1), 131 (2), 128 (1) Ritmo (1) X1/9 (2)
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bartigue
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Re: IDF dimensions

Post by bartigue » Fri Sep 06, 2019 6:25 pm

If they aren’t Weber then what are they,
Empi? Weber also made a 36 IDF in case they measure super small!
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Brad Artigue
1969, 1969, 1970, 1979, 1980, 1981, 1982, and 1982 124 Spiders
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ward00
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Re: IDF dimensions

Post by ward00 » Fri Sep 06, 2019 8:06 pm

Yikes 36mm. I'm assuming mine are Chinese. Makes me wonder if my 40 is not a 36 and my 44 is not a 40. The proper place to measure the 40 or 44 dimension will give me the answer.
Currently in Santa Cruz, Ca
75 Spider - 1.8 with IDFs running like a champ - starting performance race upgrade to 2 liter
75 Sport Coupe restoration

Past
Spider (4), Coupe (1), 131 (2), 128 (1) Ritmo (1) X1/9 (2)
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atruscott
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Re: IDF dimensions

Post by atruscott » Fri Sep 06, 2019 8:26 pm

I own a very special Chinese IDF42..... goodness only knows how they made that - normally they do “precise” duplications.

Genuine Weber’s clearly say it
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friedman
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Re: IDF dimensions

Post by friedman » Sat Sep 07, 2019 8:31 am

Measure at the base of the carbs.
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ward00
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Re: IDF dimensions

Post by ward00 » Sat Sep 07, 2019 4:01 pm

I measured what I know is an original Italian Weber at the base/manifold end and it measured 39mm, which is close to 40 but not exactly. I'm assuming 39 means 40 in Italian.

As for the carburator that I thought was a 44, its base/manifold end also measures 40. Whovever gave them to me (I did not buy it) said they were 44. I assumed that they were 44 because the top end requires a bigger outside diameter venturi than the Italian 40 IDF does, and also because the throat in the carb body past the venturi was bigger than on the 4Italian 40 IDF.

So to try to close my query, does anyone have a 44 IDF carb that that measures 44ish mm at the base manifold end?

Otherwise, why does what looks like 40 Idf (based on the 40 dimensions at the bottom end) have dimensions that are way different at the top end from that of my true Weber 40 IDF. I would have thought that if the Chinese were to make a 40 IDF knock off, the upper throat and choke dimensions would not have been so obviously different from an original 40 IDF.
Currently in Santa Cruz, Ca
75 Spider - 1.8 with IDFs running like a champ - starting performance race upgrade to 2 liter
75 Sport Coupe restoration

Past
Spider (4), Coupe (1), 131 (2), 128 (1) Ritmo (1) X1/9 (2)
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