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Discussion Starter #1
Following comments that you can run Webers on a standard Solex manifold. I bolted the set of 45s I have on to see what would happen . Quite impressive fired up instantly on full choke and revved and held at 3,000 rpm. Close chokes and it slows down to idle blowing flames out of the intake trumpets.

So work needed . Any comments would be appreciated . Is it over jetted ?, as each cylinder will be pulling directly from two Weber intake tubes does the jetting need to be halved , Any jetting advice would be appreciated or I may just back to to Solexes

engine 28th February.jpg
 

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I guess a 2600cc 6 cylinder would need similar jetting to a 1750cc 4 cylinder e.g. DCOE40 32. What jetting and venturis do you have?
 

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Discussion Starter #3
Agreed , I have DCOE 45 s . The question was how to run these on an original siamised solex manifold . Ports 1&2 , 3&4 ,5&6 are connected together
 

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I have never heard of anyone enjoying unqualified success on a still-Siamesed manifold. Apart from a dozen other things, the front and back ports of each pair are not necessarily designed to transport equal amounts of air.

But, as we say..... "good luck with that". 👍
 

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Wondering why this causes an issue? Think about a v8 engine's manifold where people put 1, 2, 3 or even 4 carbs on a manifold and they vary from being a huge area where everything can just mix to individual ports.

I know the Solex carbs were designed to be a single throat for most of the time and when you stood on the throttle they became twin throat, hence the need for siamese ports. But with the Webers it's just twin throats all the time, just like an original Mini when you stick a single weber side draught on a 2 into 4 manifold.

Just needs the right jetting ... ?
Pete
 

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Pete,

There are a few subjects on the BB, such as gear oil, and Weber's vs FI, that should come with a Sticky similar to a biohazard or nuclear three pointed star. This is one of them, although 2000 and 2600 owners tend to be a more civilized lot than many.

The opinions vary as to why the Siamesed manifold won't work with Weber's. People have found various ways to de-Siamese them, producing various degrees of success.

The 2600 was also offered originally with Weber's, but using a manifold for that purpose. The similar early 2000 used the same concept with its four-cylinder engine, but I'm not aware of any Weber options being offered. Once the early 2000 production moved to Brazil, they eventually abandoned the dual Solex, primary/secondary carbs, and shifted to a single, two-barrel downdraft, with an option of two, two-barrel Solex ADDH side drafts, similar to one of the options on the Euro 105 cars. The manifold for this option is much like the 105 cars, and works great with Webers.

As usual, there's more to the story, but although I've heard of successful conversions with the stock manifold, I remain unconvinced.
 
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Okay I'll just watch and learn :)
Pete
 

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If you learn anything... that works.... please "splain it to us.
 
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I have never owned a 2600, nor had to deal with the Solexes, but I do understand the circumstances described here. I am imagining each pair of the six cylinders, with a siamesed intake plenum, pulling through the primary venturi of the Solex, and then through the secondary on demand. OK-- that is similar to an intake plenum with a 2 cylinder 4 stroke motor drawing from that common plenum.

Now, if we imagine that same intake plenum and cylinder arrangement, with a Weber DCOE with synchronized, equal area venturis with identical jetting, emulsion tubes and air correctors, then I think I can see how valve timing and the differing cycles of the adjacent cylinders would disturb that balance needed in the airflow.

Sorry.. just got carried away with what Walt Disney used to call "imagineering". I will lean back in my armchair here and listen to what the experienced 2600 owners have to say. I enjoy carb discussions, anyway.
 
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Alfaloco,

My first dive into Alfa siamesed manifolds and Webers was about 1975. I owned a 2000, had several friends with them, plus one with a 190SL that used the same carbs and manifold design. I worked for the US importer of Webers.

We didn't have the resources to ruin manifolds experimenting with de-siamesing, so people lived with terrible drivability until they rebuilt their Solexes and decided they weren't so bad after all.
 
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Discussion Starter #11
At the risk of rocks coming back over the wall. Would there be a logic to blocking one side of each weber as a test then the jetting and mixture should be correct ,but drawn twice per 4 stroke cycle not once, Similar to the solexes running on one barrel at low speed.

N.b I agree that the Solex will now go back on until a second inlet manifold can be de-siamised. I am just with PSK there should be a jetting set-up which would allow running?
 

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Discussion Starter #12
Or as on the Solexes . Add a second butterfly valve on each left hand tube which opens at 2-3,000 rpm . Simple mod!

The setup runs fine above 3,000 rpm
 

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Tom Zat and Joe Benson would be able to sort this out in probably a couple of sentences. I do recall it was a very big deal that the manifold was key piece if you tried to swap out the Solex for Weber carbs and Alfa did have a specific manifold for the job if I'm not mistaken. I don't know the physics but they would. I don't know how to reach either of them. Perhaps someone does. . Is is possible Larry at APE would know how to reach out to Tom and Tom would have Joe's contact? Dunno. It would be worth investigating and go to the experts for the answers, IMO.
 

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Discussion Starter #14
NB My 1964 2600 spider is running on an original Weber 6 direct port manifold , using Dellorto DHLA 40's. It still has a slight flat spot when pulling off from idle which I am still working on,

This experiment is on a second 1964 RHD spider I am working on for a friend

As photos

dellorto DHLA 40-2.jpg
 

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NB My 1964 2600 spider is running on an original Weber 6 direct port manifold , using Dellorto DHLA 40's. It still has a slight flat spot when pulling off from idle which I am still working on,

This experiment is on a second 1964 RHD spider I am working on for a friend

As photos

View attachment 1675912
Now that is a lovely motor!
 
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I will acknowledge that partial knowledge can be a dangerous thing, but...

Over decades of selling Webers for all sorts of cars, including such things as Datsun Z cars with one barrel per cylinder, and MGs with one barrel serving two cylinders, I will assert that the dynamics are just different. It is not as simple as finding the right jets.

To make matters worse....

The shapes of the 2600, and cast iron 2000, manifold runners are not all the same. The primary side was designed much like an MGB Weber manifold in seeking to distribute the air and fuel from the primary barrel to two cylinders equally. The secondary runner is designed to add air and fuel equally between the two primary runners, but NOT an equal flow overall.

The PHH44 carbs have different size venturis, and jets between the two sides, as an indicator of what the manifold runners were designed to support.

Now for some bad news and good news.

Webers, generally speaking err on the rich side. Carbs are crude metering devices compared to FI, but tuners understand that a slightly rich mixture will run, whereas a lean mixture is more likely to backfire, or miss, causing a power interruption. Thus, aftermarket conversions using correct manifolds can be tuned to provide pleasant driving characteristics, but less than admirable fuel economy.

How did Alfa, and others, achieve OK economy?

We usually describe Webers as having three circuits, idle, main, and accelerator. In truth, things are more complicated when you factor in the transition between idle and main, plus the variable contribution of the accelerator circuit. Tuning the transition from idle to main is where siamesed manifold installations typically fall over.

It is my suspicion (no one has discovered a "smoking gun" document) that Alfa figured out how to use plenum vacuum transitions to modify the float bowl overhead pressure to subtly, but importantly, affect the fuel feed during various transition conditions. For them, the entire intake side was a tunable element, not just the carburetor jets.

So, if you bolt up Webers on a stock 2600 (or early 2000) manifold, the first problem is that there will be a different air demand through the front and back barrels of each carb. At the very least, this would likely require different jetting between the two barrels. Can one achieve equal power outputs between cylinder pairs? Possibly. Interesting challenge.

How to avoid the transition "bog"? My observation from over 40 years ago was that the usual problem was a lean flat spot, not the typical rich flat spot.

So, now the possibly good news.

Some of you may recall my mention of Keith Franck, and his work on redefining the basic concepts of Weber tuning. At the heart of his work has been creating a new way to control the timing and strength of the circuit transition process. He has also created some new concepts in idle circuit management, but that is secondary to the transition control.

Redmerlin.....

Before abandoning efforts to run Webers on your stock manifold, I recommend you hook up with Keith. It is possible he would grasp the challenges of having different jetting in the fore and aft barrels, as well as the tools to solve the transition lean bog (or whatever it is).

My concluding comment is that the greatest power, and most resolved "drivability", when when using Webers will come from individual, unconvoluted, unheated manifold runners. Everything else will, in some way, be compromised.
 

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Discussion Starter #18
Don understood. just for the hell of it , I will try sticking a tennis ball on each of the Secondary trumpets and see how the engine runs on the primary only. Meanwhile I have a spare manifold to de-siamise. I did try Keith Frank before but he didn't seem keen on my Dellorto's , maybe more interested in Webers
 

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Don understood. just for the hell of it , I will try sticking a tennis ball on each of the Secondary trumpets and see how the engine runs on the primary only. Meanwhile I have a spare manifold to de-siamise. I did try Keith Frank before but he didn't seem keen on my Dellorto's , maybe more interested in Webers
keith has recently made some stuff for Dellortos, so perhaps his mood has changed. I do believe that is a factor.

I doubt covering the #2 inlet is a good test. That might have the effect of increasing the vacuum ratio on the fuel circuits in #2, but without its additional air, thus acting like an enrichening choke.

The PHH44s have an idle fuel feed and adjustment on all four barrels, so they saw some benefit from balancing the fuel flow across all four at idle.

If you want to try your experiment with the tennis ball you might also remove the emulsion tube stack from each of the #2 barrels.

If your setup was intended to duplicate the actual Weber guidance for one-barrel-two-cylinder operation, the formulas for Venturi and jet choices are quite different than 1:1. I'd be really curious how your car ran using that formula for your #1 cylinders, remove E-stack on #2, and tennis-ball the #2 inlet. My only concern would be abnormally high vacuum acting on the #2 idle and progression circuit, but that may not be a big problem in reality, and not much of a problem at larger throttle openings.
 

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Discussion Starter #20
Its not my car , so I am going back to the Solexes for now. If I started as I suggested putting tennis balls on his intake stacks the owner would doubt my sanity, Something you have to do on your own!
 
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