IDF dimensions

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friedman
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Re: IDF dimensions

Post by friedman » Sun Sep 08, 2019 8:04 am

It does sound odd, you would think a carb venturi would be bored consistent all the way through from top to bottom and adjustments made with the removable venturi. I don't have a 44 to make any measurements for you and my 40s are currently bolted to my X.
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atruscott
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Re: IDF dimensions

Post by atruscott » Sun Sep 08, 2019 9:01 am

I’ll measure some carbs later. I’ve got Italian made Weber 40 and 44, along with Spanish made Weber 40 and 44, on the shelf.
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Re: IDF dimensions

Post by fiatfactory » Sat Oct 12, 2019 5:31 am

I just happen to be overhauling a set of IDF13/15's and also a set of 44IDF20/21's this weekend... and dug out my inside dividers and measured the ID of the throats just below the butterfly plates. (not measuring the slight chamfer at the very base of the carb throat)

40IDF 13/15 measure 40.15mm I.D.
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44IDF 20/21 measure 44.20mm I.D.
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maybe the EMPI /Chinese copies are smaller?

but it looks to me like 40mm in Italian is actually 40mm...

What do the auxiliary venturis look like on the set that you thought were 44's?
The aux venturi design of the 44's is much less restrictive than the 40's

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Re: IDF dimensions

Post by ward00 » Mon Oct 14, 2019 11:31 pm

So all three sets of my dual carbs have 40ish mm dimensions at the location you measured, albeit all have appreciable variances in this measure dimension.

The one that I thought was a 44, was based on me initially measuring the throat diameter at the other end of the carb. At the top of this carb the throat diameter is 47 mm. This carb has a different appearance/design, in that it has a spacer mounted to the main carb body that expands from the 40ish throat of the main body of the carb to the 47 mm top dimension shown in the image. For comparison, my other two sets of dual carbs have an upper dimension on the order of 41-42mm

Because of the large taper, its seems that this spacer was intended to provide the function of two short velocity stacks?

I never mounted it, and now I'm sure I wont because of the unknowns. Even the Weber sticker seems suspect?

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Re: IDF dimensions

Post by fiatfactory » Tue Oct 15, 2019 3:12 am

that's an ODD 40IDF, it uses an aux venturis like a 44IDF...

and BTW, it wont run very well like that, the Aux venturi is in upside-down... the orifice the fuel issues from faces away from the airstream.... it won't pull very much fuel like that...
unpsidedown aux venturi_LI.jpg
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Re: IDF dimensions

Post by atruscott » Tue Oct 15, 2019 4:29 am

.... and that “spacer” is the carb top cover .... they all have it
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1960 Autobianchi Bianchina Transformabile
1970 238 Camper OHV
1974 124 Wagon TC
1974 124 Special TC
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1976 124 Sport Spider (The Racer)
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1985 Pininfarina Azzurra
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Re: IDF dimensions

Post by friedman » Tue Oct 15, 2019 8:41 am

Hard to tell from the picture but it looks like the upside down aux venturi would interfere with the throttle plate when fully open.
Life seems so much simpler 30 years ago when only Weber made IDFs.
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Re: IDF dimensions

Post by ward00 » Tue Oct 15, 2019 12:18 pm

fiatfactory wrote:
Tue Oct 15, 2019 3:12 am
that's an ODD 40IDF, it uses an aux venturis like a 44IDF...

and BTW, it wont run very well like that, the Aux venturi is in upside-down... the orifice the fuel issues from faces away from the airstream.... it won't pull very much fuel like that...

unpsidedown aux venturi_LI.jpg

SteveC
Ha, thats why the person I got them from (for free!) said they ran like crap. Just curious what does ODD mean. Also, does the sticker indicate they were made by a China man/woman? There are no other Weber markings on the carbs, not even on the jets.
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Re: IDF dimensions

Post by kendall » Tue Oct 15, 2019 4:42 pm

For those curious as how you might get a small/odd sized carb from a Chinese maker, the answer I would wager to guess is in shrinkage of the casting. Typically castings shrink I think around 10-15%. So in a 40 or 44 mm bore that's 1 - 1.5 mm, about what some of you saw in the cheap knock offs out there. They probably measured a carb and made their molds off of that not factoring in shrinkage of the final part.
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Re: IDF dimensions

Post by fiatfactory » Tue Oct 15, 2019 8:55 pm

friedman wrote:
Tue Oct 15, 2019 8:41 am
it looks like the upside down aux venturi would interfere with the throttle plate when fully open.
Nope, they can definitely be fitted unpside down in 44IDF and also in 45DCOE's (plus probably other models too) without the throttle plate being interfered with at all, and function, albeit very very poorly...


ODD, just odd... as in unusual / different.... because it's a mixture of 40IDF and 44IF bits, a real mongrel... but from a performance (well airflow) perspective would function much better than the stock 40IDF because of the 44 style aux venturi, and the taper to the top cover would also be a bonus, usually the 40IDF is about 38mm ID at this point... and is another of the points to address if you're chasing more performance without the desire/cost of upgrading to a larger carb / throttle plate.

If there are no EW markings cast into the carby body, then they are copies... the chinese copy evrythng but the trademark, as that's covered by international laws...

as for not using them.. well your other webers seem to have a problem with the enrichment plungers leaking... if this carb is much newer then the EP tapered seats may be in good condition and be sealing...

If you swap the internal metered components from a known weber into one of these copy carby bodies, there's no reason why it wouldn't function (if you don't install bits upside down) and with the added airflow bonus... IMO the genuine weber aux venturi design on the 44IDF will function far better than the CB prformance "spray bars" kit you've purchased as it's pulling fuel right in the centre of the carby bore, at the point of highest velocity / lowest pressure, the CB kit has a series of holes on the underside of the spray bar, and each hole would be subject to (slightly) different pressure/air speed as they go further from the bores centreline....and the CB kit totally loses the functionality of adjustment to ths metered part

SteveC
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