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Dual WEBER 40DCOE vs dual SU HS4s

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dvcasano Avatar
dvcasano Gold Member David Casano
Amsterdam, NY, USA   USA
I am currently running a single WEBER 40 DCOE (TIPO 40DCOE 149, No 4). I'm not entirely unhappy with performance but it does run rich and I can't seem to lock down the problem. What I have done is purchased a dual set of SU HS4 carbs and sent them off to Joe Curto (sp) for rebuilding.

What I would like to do is assemble a dual WEBER 40 DCOE system. Just how close do the Weber bodies need to match just in case I can't find an exact match.

The more information I read about the WEBERs the less I understand them. Quantum physics would be easier to understand.

Thanks in advance for the input.

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ima68tr Tom Fremont
MILFORD, OH, USA   USA
1968 Triumph TR250 "Jaqueline The Ripper"
Hi David,

The 40DCOE149 is one I haven't run across in 25 years of blissful Weber ownership ( and vigilance for deals on ebay ). There may be something intrinsic to it which thwarts your attempts to dial it in. Mike Pierce can tell you about that ( www.piercemanifolds.com ).

Dual ( triple, quad or sextuple ) sets must have the same numerical suffix. The most common in the size 40 are -2, -18 and -151. These have quite a following in TRIUMPH applications and others with Spitfires can chime in to help ( I've got 6-pots ).

If I ever get a Spitfire it'll wind up with twin DCOEs. So far the 1300 engine is where my interest lies. I think 90+ HP is reasonable.

Tom

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dvcasano Avatar
dvcasano Gold Member David Casano
Amsterdam, NY, USA   USA
Thanks for the quick reply.

More horsepower would be great, but all I'm looking for is a cleaner running engine. 2 cylinders run very clean and the other 2 run rich. The general consensus amongst the formuites is to leave well enough alone. I agree but it is bothering me and I would like to know it is running well rather than just getting by. I know this is probably going to come back and bite me in the arse. The old saw "fix it til it breaks" comes to mind.

My biggest problem in upstate New York is finding people who still work with carburettors for our little jems.

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Roy Avatar
Roy roy o
Marietta, GA, USA   USA
Dual webers need to have the same progression holes for idle , cruising . Everything else can be changed to match each other .

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clshore Carter Shore
Beverly Hills, FL, USA   USA
The commonly used single Weber manifold on a Spitfire is inherently flawed.
Virtually impossible to achieve equal fuel mixture between inner pair and outer pair of cylinders.

The dual SU manifold employs a crossover tube to successfully address this issue.

The issue, and the crossover solution, have been well known since at least the mid 1930's.
The 1-3-4-2 firing order creates uneven intake flow pulse pairs in each of the DCOE runners.
The carb, being mechanical, delivers unequal mixture to the leading vs the trailing pulse.

There are single DCOE Spitfire manifolds that pair together #1&#4 pulses to one choke, and #2&#3 pulses to the other.
That results in equal pulse spacing, and thus equal mixture to all cylinders.
Problem is, the runners are no longer straight through equal length, so not as effective.

The crossover tube used with SU achieves the same result, while retaining the straight through runners.
Odd that no one has developed a single DCOE manifold that uses a crossover tube.
(would not be too difficult to modify a manifold to add the crossover tube, nothing magic about them)



Edited 1 time(s). Last edit at 2019-03-12 08:00 AM by clshore.

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TheZster Avatar
TheZster Steven Z
SAINT LOUIS, MO, USA   USA
1978 Triumph 1500 "BLK-BRY"
Agree with everything above...…

As Carter mentioned - Your single intake manifold doesn't handle the distribution well.... It's not the carb - it's the intake manifold with no method of balancing distribution.

DCOE Models can vary significantly over the years - especially the number of progression holes - Try best you can to match the suffix..... As I recall (my mind is on relocation rather than re-carburation at the moment) - the early models had 3 progression holes and later models 4.

Everyone here knows my inclinations...… but - as you've already got a set of SU's being rebuilt - I might suggest you get those put on - that alone will go a long ways towards relieving your richness issue.... and run them while you study up on the Webers. They really aren't rocket science - but they can be involved and a bit frustrating. There are so many "options" when setting them up - and some of them seem counterintuitive.... add to that the lack of "user friendly"/common sense nomenclature when describing sizes of jets/tubes/etc.... it can get confusing.....

I wouldn't give up on your ultimate goal.... But I would learn all I can about Webers before spending to much $$ on a new set-up that might/might not work....

Best of luck....

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dvcasano Avatar
dvcasano Gold Member David Casano
Amsterdam, NY, USA   USA
I spoke with Pierce Manifold yesterday. He pretty much agreed with everybody on the forum. The best set up is an exact match set of Webers, which in my case may be very difficult to achieve. My No.: 4M Tipo: 40DCOE 149 was manufactured for some 1960's South African cars. He also implied it may be a long wait till either he or I find an exact match. One other thing he did mention was a balance tube could be fitted on the intake manifold to help alleviate the imbalance between cylinders. I seem to be determined to "fix this car until I break it". It looks like the SU HS4's will be installed either this year or next.

Thanks for all the great information. What a learning process this has been.

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Guppy916 Avatar
Guppy916 George G
Alton, Hampshire, UK   GBR
Hi I run my GT6 on a set of triple 40's Details are :-
Front 40 DCOE-3 4L-01
Mid 40 DCOE-4 8C-02
Back 40 DCOE 2 7D-01
So mine don't match, at the moment they are on a set of jets that I choose just to get them running fair ish
Was 30 Chokes
6 Aux Venturi
59F21 Idle Now F8-55
85F9 Starter Jet same
35 Accelerator Pump Jet same
150 Air Correction Jet 160
F47 Emulsion Tube F11
150 Emulsion Tube Holder ?
120 Main Jet 115
I need to do another 50 miles then it's onto the rolling road, it's running a lot better with no spitting back and no flames out the trumpets, i do have a set of K&N's ready to fit



Edited 1 time(s). Last edit at 2019-03-13 03:11 PM by Guppy916.


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rich wino Richard Ruggiero
wallingford, CT, USA   USA
Hi dave is your engine stock or have you made upgrades such as cam compression head port and polishing headers. If not Pierce has a kit for stock engines. If you already have the carbs than they can help you with getting the right combo of jets emulsion tubes and so forth It could be a long and arduous journey but might be worth it. Yes su's might be easy but two weber 40's can be dialed in to be the best for performance and it has the look. Once you have the gas air mix perfect it is all about the look!

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dvcasano Avatar
dvcasano Gold Member David Casano
Amsterdam, NY, USA   USA
I already have what is evidently a unique and rare version of the 40DCOE carb, so I think will leave well enough alone for the time being. The only suggestion that sounds doable for the time being is put hotter plugs in 1 & 4 and see if that alleviates the rich running cylinders.

By-the -way, if anybody runs into a WEBER 40DCOE Tipo 149, No. 4M, I'm a motivated prospect.



Edited 1 time(s). Last edit at 2019-03-13 04:23 PM by dvcasano.

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