In my opinion, the best rendition of the setup is still the page from the parts manual copied below.

The first picture of the cross-over tube with the air filter attachment is from eBay auction #290365429185, which ended today at USD 266.01. This is either an original Weber cross-over tube or a very good conversion.

The second picture is from the eBay auction of AR192605 several years ago. I might be an original setup (if it is, then the two hose brackets on the plenum would be missing). I know the current owner but never got around to taking close-up pictures of the adapters between plenum and carbs.

Unfortunately, Bob Piacentini's web site about Weber conversions no longer exists. Pictures of his car with converted Solex manifold are in this thread.

 

weber conversion

Thanks Tubut..your are always so knowledgeable ,
Others please do no hesitate to post more pictures or infos..
Regards
Herve

 

I doubt that I can add much that has not already been covered, but here are some pictures of my Weber set-up. The manifold is the correct Weber and the carbs are 45 DCOE 9. When I got the car in 1971, it had no air plenum and no air cleaner. It was using air horns with screens on their ends. I made the adapter plates to mount the air plenum and also modified the air cleaner cross-over tube for the hoses to the float bowls. I am still struggling to eliminate the dreaded flat spot around 2000 RPM. The parts book shows a different number for the air plenum used on the Weber set-up and I assume it had round outlets, to match the Weber carbs, and maybe no vent holes for the float vents of the Solex carbs. About two years ago, there was a plenum listed on eBay that appeared to have round outlets. It was in Australia.
Larry

 

weber set up

Thanks Larry..
You are one of the lucky ones with a correct weber intake manifold.
How is the driving experience ? Maybe you can share a little bit of how you think the car drives with the webers?
Regards
Herve

 

Flat spot

Have you tried the progression hole fix as suggested in another thread?

 

If the "progression hole fix" involves drilling a third or even fourth progression hole in the carburetor, it is most likely not a good idea. Many if not all of the critical orifices in a Weber carburetor are sized based on theoretical flow rates for orifices of the specified dimension. In other words, a 1.55mm main jet is not necessarily 1.55mm in diameter. It is whatever size the factory determines on a flow bench is needed to actually flow the amount of fuel which a perfect orifice of 1.55mm should flow. Thus, the hole size could vary even between jets labeled the same size, as long as factory QC testing determined that the jet's actual flow rate was within spec. The use of "jet drills" to resize Weber parts is therefore strongly discouraged, because it is likely that a jet which is simply "drilled out" to a certain size will not flow to spec.
Similarly, if a new progression hole is drilled in a DCOE, there is no way to determine the actual flow rate for the new hole without a flow bench. More important, without testing there would be no way to determine whether the same hole drilled in a second or third DCOE produced the same flow rate as the in the first carburetor. In other words, the "progression hole fix" could lead to seriously unbalanced carburetors and even more difficulty in smoothing out the progression phase. Finally, a DCOE with a drilled third progression hole would not be interchangeable with a factory unit with three progression holes, and therefore of little value on the open market.

 

I agree with Lock about modifying progression holes. I have not yet exhausted various combinations of jets, etc. because of the expense, but would not attempt other modifications because I am not qualified. There was some discussion on the Yahoo Group about jetting when using air horns and without the air plenum and how much better the car performed. When I got this car in the 1970s, it was using air horns with no air plenum or air filter. My memory may be spotty from that era, but I do not remember a problem with flat spots in the acceleration. At that time, the jetting in the carbs was the same as is shown in the Haynes Weber Manual for a 4 liter Aston Martin. I also remember a comment from someone who claimed his car would not even run if the Weber float bowls were vented to the air plenum rather than to the crossover tube! My guess is that a lot of our problems have to do with the air plenum.
Larry

 

At this point I am wondering why we should need the hoses that go to the cross over. Why not simply make an adapter plate with a screen (a faucet screen should work). Considering that the air horn set on Lock Holmes car does not even have screens or the float ball vent, a screen might not even be necessary.Jay Nuxoll made that suggestion to me , and it make a lot of sense. The problem with venting the floats through the plenum , is probably due to the fact that the air gets sucked out of the floats. I will be experimenting after christmas and will post my findings. I have a newly rebuilt solex set up and I am making a weber set up to see what runs best on the same fully rebuilt engine(using new 45 dcoe from pierce)
Herve

 

Weber mods

Their should either be screens over the float vent if using Airhorns ( keep out particles), or the carbs must be vented to the inside of the airbox so that the same ambient pressure feeding the inlets is also above the fuel. Otherwise the fuel mixtures will never be consistant and approiate to airflow.

 

I agree with Richards comment, as follows:

"the carbs must be vented to the inside of the airbox so that the same ambient pressure feeding the inlets is also above the fuel. Otherwise the fuel mixtures will never be consistant and approiate to airflow."

I believe this is what Weber intended and if you look at any other application, these pressures are balanced. Whether you are using the stock plenum, a custom filter, or no filter at all, the pressure in the float bowl should be the same as that feeding the inlets.

Here's some empirical evidence: My car was running pretty well with just horns and no filter of any kind. When I tried to bolt on the plenum and vent the float bowls to atmosphere, the car would barely run at all. As soon as I connected hoses from the plenum to the float bowl vent, it ran just as well as it had with the horns only.

The thing that seems unique about the 2600 is the hoses that go all the way to the crossover tube. All of the other Weber setups I'm familiar with don't do this. Typically, the float chamber is vented directly to the air cleaner box through the third (smaller) hole in the carburetor flange. This is how my Maserati 3500 is configured.

Not sure what Alfa was thinking, but nobody else seems to have followed their lead on this.

 

Here's some empirical evidence: My car was running pretty well with just horns and no filter of any kind. When I tried to bolt on the plenum and vent the float bowls to atmosphere, the car would barely run at all. As soon as I connected hoses from the plenum to the float bowl vent, it ran just as well as it had with the horns only.

Hi
The verdict is do not connect the spacer plate used with the weber set up to the air plenum. IF you have do yourself a favor, disconnect it and your car will run 100% better. The float chamber should be at ambient pressure and if you want to connect it somewhere the original set up (cross over pipe) will work also. We ran that test on richard Ott car and the car runs like a dream. He uses a disiamised solex intake manifold and 45dcoes...You can also mount a little screen if you want to avoid any debris from falling inside...
Regards
Herve

The last two posts seem to be in direct contradiction. Richard Ott's car (if it's the car I know about) would be the ex-Bob Piacentini RHD Sprint shown in this thread with vents attached to the Solex plenum (not to the cross-over tube). If it's indeed the same car, I hope we can figure out collectively why the plenum air setup works in one case but not the other and/or why the vent would be so sensitive that it makes a difference whether or not it's attached at all or to the plenum or to the cross-over tube. Furthermore, is this a known issue with DCOEs or is this happening only on 2600 engines?

 

Hi
The verdict is do not connect the spacer plate used with the weber set up to the air plenum. IF you have do yourself a favor, disconnect it and your car will run 100% better. The float chamber should be at ambient pressure and if you want to connect it somewhere the original set up (cross over pipe) will work also. We ran that test on richard Ott car and the car runs like a dream. He uses a disiamised solex intake manifold and 45dcoes...You can also mount a little screen if you want to avoid any debris from falling inside...
Regards
Herve

 

A note on progression holes

I agree with Larry and Lock that modifying progression holes should not be taken lightly. They're right about the fact that Weber specs are fairly narrow and should not be fooled with. However, this is exactly where two significant constraints of factory specs come into play:
1. The factory specs were for Weber 45 DCOE 9 carbs on a Weber manifold.
2. Fuel specs have changed dramatically since the early '60s when they used leaded fuel on the flow bench and such specs are probably outdated.

Today's reality seems to be that in most cases, we're talking about (a) using Weber carbs on a modified Solex manifold and (b) adapting Weber carbs that were spec'ed for another engine (e.g. some kind of Weber 40 carbs from a 4-cyl Alfa or maybe even some 45 DCOE 152 carbs) to the 2600. Since there are no official specs for such adaptations, we'll have to grow home-grown specs.

This post explains the concept of the progression hole fix. Lock's call to caution is good advice -- mistakes are practically impossible to correct. There's a chance that drilling additional progression holes could make things a lot worse if the existing holes are already over-sized.

Methinks, what we need is a few people willing to try what works and what doesn't. In this context, finding an answer to the question "Have you tried the progression hole fix as suggested in another thread?" seems quite valid but, as contradictions in other recent posts seem to suggest, any and all results must be taken with a grain of salt -- until verified by others.

Since all results somewhat depend on what the original carb specs were (e.g. the original number, location and size of the progression holes), it might be a good idea if we start documenting who is using what type of carbs and what their serial numbers are (serial numbers because I'd expect some variances among carbs with the same designation).

What I hope for is that we'll develop some kind of fool-proof recipe for adapting Webers to our cars. I've always been an optimist.

 

Hi Ruedi
Yes you are correct about Richard Ott's car, it is the one you indicated in the above thread. The float vents were connected to the air plenum. So removing that connection made the car a much better driver. Rich has also an original cross over pipe for the weber set up with the small hose pipe fittings, so we will run some hoses to the floats vents and see if that produces any changes.
Regards
herve

 

Weber air piping

Hi . I thought I'd restart this old thread because I now have all the parts to build up the weber manifold and air piping .

The pictures in this thread help a lot but does anyone have any pictures of an original 2600 Weber installation? Also where the three air pipes exit the main air intake cross tube - what happens inside?
Do they turn at 90 degrees again to face into the air flow - this seems logical as all three pipes would then get a similar pressure

thanks

Ian

 

Ian, I posted pictures of an original Weber air plenum adapter plate in this thread . The picture was taken on what I considered to be an original Weber setup consisting of manifold, carbs and air plenum adapters, but when the owner found it, the original air plenum and crossover tube were missing.

Franco posted pictures of what looks like an original crossover tube here, two posts above in the same thread. I know I bid on at least one of them on eBay but was outbid (Herve may have won the auction). I have a hunch that the three pipes in the original Weber crossover tube extended all the way to the edge of the air filter hose attachment, but I have never been able to inspect an original Weber crossover tube to verify that notion.

I posted some info on the history of Alfa extending the Weber float bowl vents towards the air intake (and some speculations as to why it may be a historical artifact, carried forward from DCO3 carbs, but possibly unnecessary on DCOE carbs) in Don's thread here.

 

Thankyou Ruedi. I will follow the full length pipe theory it seems logical to me

 

Hi Ian
Do you still have your original solex carbs? If you do .....spend the money on restoring them
Unless you have an original weber manifold , the car will never run as well as the original carbs. plenty of parts to rebuild them are available from mercedes 190sl part suppliers...
I have spent thousands and many hours doing both..and the car always ran great on solex and as far as power gain with webers..i was never under the impression there was any....
cams , valves and pistons..that is where you can gain a few horse power(mostly at the top end)..so you will have to rev that motor high to notice...
I understand that Lock Holmes was going to remanufacture the original manifolds..If he has ..get your hands on one...
if you are going to de siamese the original manifold ,,be prepared for a lot of frustration and the dreaded power hole below 3000rpm...
Furthermore, by keeping the car original ..you will preserve it the way it was intended to be...
Have fun
Hervé

 

Hi everybody,

Sorry Hervé, but I don't agree with you.
I have converted my 2600 Touring with weber and the result was much better than with the Solex.

This conversion was a real pleasure to do.
The de siamese was easy to do,
The plate for the new fixation of the accelerator cable too,
I bought the 3 plate for air intake at Touring63 (I really don't like the look with the original air plenum).

I use the same setup than the 2L 105 type engine ("smaller" Weber) and the behavior of the car was perfect. Before I sell the car at Le Mans many people test it (specially Arcurial guys). Everybody where astonished by the engine behavior.

I strongly recommend this conversion...

Serge.

 

2600 carburetor conversion

Hi Serge
since you were able to do what i was not able to achieve. Please educate me and all other participants to this thread.
What size webers did you use. 40 or 45?
The weber you use were original or newly reproduced?
did you perform any modifications on the weber carbs ?
What was the jetting on the carbs? Please indicate> main jet size, idle jet size,pump jet size,air corrector jet size, emulsion tube size(f1---f9) , and choke main venturi size.

Did you vent the webers through the plenum or through the cross over pipe as per original?
Did you perform any other modifications to the engine? like cams or larger valves.
This could prove to be very valuable to those attempting to convert to webers.
Thanks
Hervé

 

Hi Hervé,

The Weber are 40 not 45.

They are new one (next time I will use rebuild one - for my 2000T for example).

Here is the configuration (in french ...) :
3 carburateurs DCOE 2 :
- Buse : 33 mm
- Gicleur principal carburant : 120
- Gicleur Air : 150
- Tube d'émulsion : F 16
- Ralenti : 50 F 9
- Pointeau : 200
- Fond de cuve : 55

Here is a picture of the engine (I should have better. But I don't have them right now) :

You can see that vent is "direct".

You have here some picture of the adaptation :

http://www.alfabb.com/bb/forums/1900-2000-2600-1950-1968/308545-new-alfa-bb-4.html

Engine work :
New cylinder,
New pistons (but with the same compression ratio)
New valve and spring (normal valve)
Balanced crankshaft

That's all ...

 

I forgot :

New NGK spark plug
123 Ignition
New wiring

Driving the car were just magic ...

 

Hi Serge
Bravo..very nice job
so for everyone trying to do that conversion..try using 40 dcoe..my mistake is that i stuck with 45dcoes..probably too big for the engine. using 45dcoe was apparently the original configuration with the original weber manifold.But with the sole 40dcoe must be the right set up..
If you have not sold the car yet..I hope you do well..you have put a lot of effort in this restoration.
Sold my 2 restored 2600 spiders..now concentrating on my dino spider 2400
Thanks for your very detailed answer..
Hervé

 

I have sold the car ... unfortunately.

I assume that the 40 DCOE is the solution (45 is too big ...)

The Dino Spider is a very nice car. Good luck and a lot of fun.

Serge.

 

I should note....

I'm using 45DCOE9 on my 2300, with 35mm chokes. I was expecting a loss of low RPM drivability/torque. The cams that RJ recommended add lift, but reduce the overlap. I have at least as much low rpm torque as originally, when I was using 40DCOM and 33mm chokes, but much more torque all the way to redline.

The early 45s are flexible to tune. The later have more complexities intended to improve emissions.

The 2300 has roughly 33% more cc per cylinder, which is directly relevant to choke size. The cylinder volume of the 2600 would indicate a 30 or 31 mm choke if using a similar cam as mine. I believe this cam change would be very good for the 2600.

A 33 choke should be fun if one is happy to accept a little loss of low rpm torque. With the 6 cylinder nature, this slight low rpm torque loss would probably be no problem.

 

Unfortunately, Bob Piacentini's web site about Weber conversions no longer exists.

That's not entirely true...but I'll explain later.

Back in 2001 Bob Piacentini de-siamesed a Two-Liter Solex intake manifold for a Weber conversion for S/N... 00310. He was very specific that routing the float chamber vents into the cross-over tube had created some serious issues for him and should be avoided. Perhaps the open ends of the tubes were parallel to the airflow and not perpendicular to the airflow like the original Weber manifold cars.

For what it is worth, I printed out a copy of Bob's web site and while he does not go into a lot of detail about the float chamber vent, he does reference it related to an article on page 22 of the March Alfa Owner. Unfortunately the last four letters or digits of each line were cut off by the printer but I am pretty sure the year was 2001. Bob was pretty straight forward in describing exactly how the Solex manifold could be de-siamesed, giving precise details and photographs.

If it would help anyone, I'd be happy to scan this print out and post. Also, ...00310 is running 33 mm main venturies (choke tubes) and despite protests from many 'Weber oriented' friends, does not seem to mind.

Mark