Weber IDF 40 carbs linkage arm on carb wrong in K 291XE

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Chris Macie
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Re: Weber IDF 40 carbs linkage arm on carb wrong in K 291XE

#16 Post by Chris Macie »

C J Murray wrote:They are easy to fabricate.
Have you something like a mechanical drawing / spec of how they should turn out?

Chris Macie
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Re: Weber IDF 40 carbs linkage arm on carb wrong in K 291XE

#17 Post by Chris Macie »

Weber 40 IDF carburetors – more details, analysis (and perhaps confusion)

As it turns out, what I'd initially bought was a pair of "18950.138" carburetors, thinking they would be simply the same as in the K291XE kit sans the air filters, gaskets, bolts, etc. That is the case, EXCEPT for the linkages. The 19850.138s are pictured at times (on the internet) with a proper "push-down" type linkage at one end – a "right-side" carburetor – but other pictures show the "pull-across" type linkage at both ends (useless on Porsche engines). This latter is the case on the carbs that were sent to me.

One solution to that, as later learned, would have been to also purchase the adapting linkage levers 99005.314 (right) and 99005.315 (left) – an extra $40 or so. But then the ball-joint connectors ("Heim joint", or "Rose joint" in the UK) would also still be lacking.

As mentioned, I arranged to return the 18950.138s and ordered the K291XE kit. In this kit the carbs appear to have the correctly placed levers AND have the ball-joints. The only difference I can see is that the fuel line input on the left carb requires the input tube from the front. (The Weber carbs already on the car have fuel line input on both sides that attach to input tubes from the back – part of that mirror-image left-right setup Weber originally produced for Porsches.) Will do more research, see if perhaps the fuel-input assembly can be reversed on one carb.

Two other issues still up in the air:

1: Throttle-return springs.
Why is any additional spring necessary when the Webers have already a rather heavy-duty looking spring coiled around the throttle shaft, at one end or the other?
BTW: One commentator (in a youtube video on sync-ing IDF carbs) mentioned that the coiled spring should always be on the same side as the throttle linkage; otherwise the throttle shaft is subject to additional, perhaps over time damaging, torsional stress. One wouldn't want that – remember the age-old issue of split vs solid throttle shafts on the Solex carbs?

2: Different lateral displacement of the carbs (right side more towards back of car):
By my measurement, the difference is about 3.2cm (1.25 inches). Two possible solutions:

A: Get this 1 1/8 inch (a bit less than 3cm) Heim Joint Extension to install on the left carb:
http://vwparts.aircooled.net/SearchResu ... +extension

B: Just take the Heim ball joint off the lever on the right side and re-install it on the other side of the lever (towards front of car), and twist the end of the connecting rod around ½ turn (the change in overall length of the rod should be less than 1mm) . It looks as though there's enough space between the frontward side of the lever and the carb itself. The distance from the center of the Hiem joint to the lever is about 1.5cm, so switching sides would about match the 3cm difference to be resolved. In this option, the vertical rods that attach on both side have a more true vertical orientation, which would seem more efficient (less long-term stress on the parts) than in case A (above), where both descending rods would be something like 15 or 20 degrees slanted.

This reversing the ball-joint is shown in the photos above from C J Murray – but then why are the extensions necessary on both sides? Btw: What a beautifully clean engine in those pictures!

~C: From another perspective, how is it the engineers at Porsche didn't consider this issue in the first place (design phase)? Is it in fact insignificant? Note: it appears that the ball-joints are not removable from the linkage levers, not reversible (as in B above) on the original Solex P 11 40 carbs.

Somehow, these days many people think it's a problem worth solving, as many internet / youtube posts show the use of various extender schemes on the linkages – on VW, Porsche, and "pan-cake" (914 and VW bus) engines.

I will report back on progress when trying to install the K291XE carbs...

Chris Macie
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Re: Weber IDF 40 carbs linkage arm on carb wrong in K 291XE

#18 Post by Chris Macie »

(Refining info in Mon Nov 12, 2018 6:55 post)

A photo in an ad on page 8 of the latest Registry magazine (42-6 Mch/Apr 2019) shows an engine with Weber carbs, and

1) the linkage to the one on the right (cylinders 1+2) looks like it's simply been twisted around 180 degrees and fitted to the ball-fixture on the carb arm that's also been switched around so the ball-part faces in towards the carb body.

2) no sign of extra/added springs to the throttle arms; one can see on the right-side carb the built-in heavy-duty coil spring assembly is on the back (visible) side. (On the left carb (#3+4) the spring assembly is, presumably, on the other, non-visible side (towards front of car.)

3) looking over the new carb set, seems no reason the fuel-input set-up can't be simply re-configured (remove, replace the nozzle that attaches to fuel line on other side) such that both side use fuel-line input from the backside of the engine (the way it's set-up with the old carbs).

Haven't started the big switch-out of the carbs yet, but will report when it comes down. 8)

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Wes Bender
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Re: Weber IDF 40 carbs linkage arm on carb wrong in K 291XE

#19 Post by Wes Bender »

Re. the return springs. Whatever system you decide to use, make sure that the springs are strong enough that, should the spring on one carburetor break, the spring on the other carburetor is strong enough to return both carburetors to idle.
Some days it's just not worth chewing through the restraints.....

Chris Macie
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Re: Weber IDF 40 carbs linkage arm on carb wrong in K 291XE

#20 Post by Chris Macie »

Good point (Wes Bender re return springs).

Memories of being half-way across country, in the middle of nowhere, in the 1961 Cabrio when one spring on the Solex P11-40s broke. Was able to use pliers to reshape each broken end to hook them back together and get back on the road.

Two such trips -- SF to East Coast in 48 hours. That's a bit more than 60mph average speed, including food, fuel stops and one short nap on a sunny lawn at a truck stop somewhere in Nebraska. But one has to have the right tools along -- as in once having to adjust the valves on the side of the New Jersey Turnpike near NYC.

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