I've looked but have not found a definitive answer so here goes.... what is an emmission dcoe weber carburetor? Is there a difference between a dcoe 151 made in spain and one made in Italy? Some of what I gather is yes, there is a difference but looking at the parts list I don't see any difference. Thanks!
gigem75
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The fundamental difference between emission Webers and "classic" Webers is in the progression circuit. Emission Webers, like most other non-DCOE Webers draw the fuel from the well. Classic Webers draw the fuel from the float chamber. At larger air flows the pressure in the well is lower than in the float chamber and the progression circuit rolls off in Emission Webers. At WOT and high revs there can be reverse flow in the progression circuit as the pressure in the well is lower than the pressure at the progression holes. Then air is drawn into the well through the progression holes. I think this is the reason for emissions Webers using smaller air corrector jets.
The progression circuit contribution is additive to the main circuit in classic Webers and it is not additive in emissions Webers. This is the reason that emission Webers need larger main jets than classics. The F34 emulsion tube that is commonly used in emission Webers is similar to the F4 that is used for alcohol fuels in classic Webers. This tube occupies less volume in the well and the fuel level is less affected by pressure transients in the well. Emissions Webers also use idle jets with much larger air orifices. It is important to have the appropriate emulsion tubes and idle jets in emission Webers.
Although John Passini's books do not cover emissions DCOE's this interaction of the main and progression circuits in other types of Webers is explained.
The main circuits of emission and classic Webers are AFAIK identical and I do not see any reason why emissions Webers should produce less power than classics of the same size.
One thing that puzzles me is the classification of 40DCOE150/151's as emission Webers as they use the same emulsion tubes and idle jets as classics. It is my understanding that they have progression circuits fed from the float chamber. Maybe they are a hybrid design?
The progression circuit contribution is additive to the main circuit in classic Webers and it is not additive in emissions Webers. This is the reason that emission Webers need larger main jets than classics. The F34 emulsion tube that is commonly used in emission Webers is similar to the F4 that is used for alcohol fuels in classic Webers. This tube occupies less volume in the well and the fuel level is less affected by pressure transients in the well. Emissions Webers also use idle jets with much larger air orifices. It is important to have the appropriate emulsion tubes and idle jets in emission Webers.
Although John Passini's books do not cover emissions DCOE's this interaction of the main and progression circuits in other types of Webers is explained.
The main circuits of emission and classic Webers are AFAIK identical and I do not see any reason why emissions Webers should produce less power than classics of the same size.
One thing that puzzles me is the classification of 40DCOE150/151's as emission Webers as they use the same emulsion tubes and idle jets as classics. It is my understanding that they have progression circuits fed from the float chamber. Maybe they are a hybrid design?
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additional differences
Here are some other differences that I have remembered since my previous post.
1 - Emissions DCOE's typically have idle air bypass screws which allow a controlled amount of air to bypass the throttle plates. They are used to precisely balance the air flow to adjacent cylinders at idle.
2 - Emissions DCOE idle jet holders have O ring seals that I assume are to eliminate air leakage past the threads which could cause small imbalances between cylinders at idle.
3 - my 40DCOE116/117's do not have screwed inspection covers over the progression holes. These ports are plugged with steel inserts. Again, I assume that this is to eliminate potential idle imbalances due to air leakage around the threads of the screwed covers.
I keep the idle air adjustment screws fully closed and I use the correct idle jet holders so the only practical consequence of these differences is that I cannot balance the Webers by observing the position of the throttle plates over the progression holes.
I prefer emissions DCOE's because they run leaner on the progression circuit and they keep the plugs and combustion chambers nice and clean. They also produce better gas mileage. I saw an improvement of at least 10% when I switched from 40DCOE24's to 40DCOE138/139's. Both my Spider and my GTV averaged about 26 mpg with emissions Webers and moderate lift cams and my current hot motor averaged 22mpg over 600 miles at 75-80 mph.
EDIT:
Emissions Webers have idle mixture screws with a slower taper and the "standard" setting is about 3-4 turns out instead of 1-1.5 turns.
DCOE151's appear to be classic type Webers with respect to the plumbing of the progression circuit but they have the slow taper mixture screws and idle air bypass screws of emissions DCOE's.
Here are some other differences that I have remembered since my previous post.
1 - Emissions DCOE's typically have idle air bypass screws which allow a controlled amount of air to bypass the throttle plates. They are used to precisely balance the air flow to adjacent cylinders at idle.
2 - Emissions DCOE idle jet holders have O ring seals that I assume are to eliminate air leakage past the threads which could cause small imbalances between cylinders at idle.
3 - my 40DCOE116/117's do not have screwed inspection covers over the progression holes. These ports are plugged with steel inserts. Again, I assume that this is to eliminate potential idle imbalances due to air leakage around the threads of the screwed covers.
I keep the idle air adjustment screws fully closed and I use the correct idle jet holders so the only practical consequence of these differences is that I cannot balance the Webers by observing the position of the throttle plates over the progression holes.
I prefer emissions DCOE's because they run leaner on the progression circuit and they keep the plugs and combustion chambers nice and clean. They also produce better gas mileage. I saw an improvement of at least 10% when I switched from 40DCOE24's to 40DCOE138/139's. Both my Spider and my GTV averaged about 26 mpg with emissions Webers and moderate lift cams and my current hot motor averaged 22mpg over 600 miles at 75-80 mph.
EDIT:
Emissions Webers have idle mixture screws with a slower taper and the "standard" setting is about 3-4 turns out instead of 1-1.5 turns.
DCOE151's appear to be classic type Webers with respect to the plumbing of the progression circuit but they have the slow taper mixture screws and idle air bypass screws of emissions DCOE's.
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F41 & F47 are almost identical. F41 has an outside diameter of 8.1mm and F47 has 8mm. Everything else about them is the same. F41's were fitted to Webers intended for 1300/1600 motors. I ran with them in a 2L motor and they were OK until I installed RJ cams, then I could not tune out lean operation in the main circuit. F34's solved that problem.
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A couple of weeks ago I had been thinking about starting a thread about the differences between emissions and classic DCOE's then I saw this thread and I started to post this information. I have details on idle jets that I want to post. My question is: should I add it to this thread given that it has drifted into a general Weber thread that is not specific to emissions DCOE's?
Thanks.
Thanks.
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Weber manufactured a series of 40DCOE carburetors that were supplied as original equipment on cars that had to comply with emission standards. These are commonly referred to as emissions Webers. The number series, I think, starts with 40DCOE72/73 and ends with 40DCOE138/139 but there are carburetors within this number series that are not emissions Webers (for example 40DCOE84 - 40DCOE89 which were OE on certain BMW's). AFAIK 40DCOE151's were not OE carburetors and they were manufactured for the replacement/conversion market. They have much more in common with the old "classic" Webers - 40DCOE3 - 40DCOE32.
I have driven over 120K miles in three Alfa's with emissions Webers and I have got to know them pretty well. I have not owned a 40DCOE151 and all I know about them is what I have read. My plan was to share first hand information of emissions Webers.
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Appendix 1 of the Haynes Weber manual lists OE carburetor configurations. Unfortunately 130/131 and 138/139 are not listed. 106/107 is shown as having no accelerator pump bleed back but 72/73, 76/77 and 82/83 have them.
38DCOE110/11 that were fitted to Ferrari 400GT's also show no bleed back.
I cannot find any references to different length pump jets.
I buy my jets from Alfa1750 on ebay. He is in Italy. He knows emission DCOE's.
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Hi Gasolina,
That is good information. For which Alfa is this specification?
I had a pair of these Webers. They were supplied by Shankle as part of a conversion kit. They had 6mm auxiliary venturis which is unusual. They also had these unusual main jets - 138 and 59F21 idle jets.
That is good information. For which Alfa is this specification?
I had a pair of these Webers. They were supplied by Shankle as part of a conversion kit. They had 6mm auxiliary venturis which is unusual. They also had these unusual main jets - 138 and 59F21 idle jets.
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You usually have to increase the main jet by 5 when you go up 2 mm in venturi size. Nothing else is likely to change. If you see an improvement it is likely to be at higher rpm.
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32's are not too big - they were standard on 1750's with mild cams.
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Some people have had problems with 45 151's that were fixed by drilling an extra progression hole. Richard Jemison is one person who has done it.
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That may well be the case.
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40DCOE 120/121 were fitted to Simca 1000 Rallye 3 according to http://gazoline.net/forum/technique...ion_des_carburateurs_par_Constructeurs_et_modeles_de_RENAULT_a_fin_de_liste.pdf
This list also shows other emissions Weber applications.
This list also shows other emissions Weber applications.
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Idle jets for emissions Webers
Here is a list of the idle jets that are used with emissions Webers. The outside dimensions of these idle jets are the same as the more common F1 - F16 range and the fuel orifice numbers have the same meaning. A 50F11 and a 50F22 both have a .50 mm fuel orifice. The internal bores are different. The early, common types have a single diameter bore which varies between different F number jets and ranges from 1.4 mm to 2.10 mm.
Emissions types have a stepped bore. The upper bore is always 3 mm and the lower can be 2.00 mm or 2.1 mm. The total area of the air orifices of emissions type idle jets is in a higher range than the early types. In other words, the richest emissions idle jet is leaner than the leanest early type.
F # holes Diameter
19 1 1.2 Rich
23 1 1.25
25 1 1.5
24 1 1.55
27 1 1.6
26 2 1.25
17 2 1.35
21 4 1.1
18 2 1.6
22 4 1.2 Lean
Here is a list of the idle jets that are used with emissions Webers. The outside dimensions of these idle jets are the same as the more common F1 - F16 range and the fuel orifice numbers have the same meaning. A 50F11 and a 50F22 both have a .50 mm fuel orifice. The internal bores are different. The early, common types have a single diameter bore which varies between different F number jets and ranges from 1.4 mm to 2.10 mm.
Emissions types have a stepped bore. The upper bore is always 3 mm and the lower can be 2.00 mm or 2.1 mm. The total area of the air orifices of emissions type idle jets is in a higher range than the early types. In other words, the richest emissions idle jet is leaner than the leanest early type.
F # holes Diameter
19 1 1.2 Rich
23 1 1.25
25 1 1.5
24 1 1.55
27 1 1.6
26 2 1.25
17 2 1.35
21 4 1.1
18 2 1.6
22 4 1.2 Lean
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If you decide to use different Webers then I suggest that you find some rebuilt Italian emissions Webers such as 40DCOE116/117 or 40DCOE138/139
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