[Brandman]

Hello, i agree with alfaparticle. The emulsion tubes are the fundamental differences between classic and emulsion carbs. The additional progression holes requieres a bigger main and a smaller correction jet. The emulsion is better than in classic carbs.
F41,F47, etc. are also tubes für emulsioncarbs.
Some emulsion carbs (138/139 or 106/107 needs a auxiliary venturi size 6.
In my opinion the DCOE 151 isn´t a emulsion carb.

Does anybody know the importance of the right reference pressure in the float chamber ?
(level of fuel in float). Thanks.

 

[Gasolina]

Hello Brandman, Do you mean "dynamic float level" ?

 

[alfaparticle]

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.

 

[alfaparticle]

F41,F47, etc. are also tubes für emulsioncarbs.

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.

 

[Brandman]

Hello Gasolina, maybe it´s (dynamic float level) the right description for that what i mean.
I´d like to get the float level pressure from the "clean side" of the airfilter,the same as in the serie-airbox. In case of trumpets (about 4-5 inches) in the airbox: is the simple hole in the groundplate (connection between flot chamber and airbox) enough or do i need extension pipes up to the trumpets ? Or doesn´t it matter ? Thanks.

 

[Gordon Raymond]

All you need is equal ambient air pressure in both bowls. Do NOT connect this to a source of of pressurized air.

 

[gigem75]

DonP, any tail dragger is a friend of mine, I've got 4 32's on the way and will give them a go. I put 135 mains yesterday and it feels like I'm headed in the right direction. I realize changing just one item is rarely the final answer but dealing with the added possibilities of more than one change at a time is above my pay grade.

 

[DPeterson3]

I'll defer to Gordon et al for tuning guidance. I did a lot of it in the 70's, but won't claim my memory is as sharp as it was then. Plus, when I gave up Alfas at the end of the 70's I gave away all my manuals and notes. I'm happy doing my own cars, and encouragement to others. Good luck with it.

 

[alfaparticle]

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.

 

[gigem75]

Six of one half a dozen of the other although a new one couldn't hurt. As was discussed in earlier posts emmision weber is almost a misnomer. A more accurate description might be "modern" weber vs "classic" weber? Either way the information would certainly be appreciated. I should note this motor had been running spica forever and was switched to webers simply because a flat spot at 4k causing detonation that could be tuned out but left all other rpms way to rich. Bottom line is the motor is not stock and I'm in the process of matching the webers to this motor. I should have stated I'm not married to any particular configuration as it's all new to me with this motor. After the 130's, I tried 135's (big difference, good) added 45 F8's today as Pat's book recomended after his diagnostics, next on the agenda are 32's to see about the top end.

 

[alfaparticle]

As was discussed in earlier posts emmision weber is almost a misnomer. A more accurate description might be "modern" weber vs "classic" weber?

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.

 

[Brandman]

It´s a good idea to collect/share this special informations about emission carbs.
For example: do all of them need the short version of the accelerator pump jet ?
Or some of them don´t have a pump back bleed. (106/107 , 130/131, 138/139, ....... ? )
And also the other "design" of the idle jets you talked about. I never wouldn´t change an emissions carb to a classic one. They work very,very well.

 

[Brandman]

By the way: i am looking for 0.30 Pump jets ,the short version. But it´s difficult to get them in europe. Does anybody sell them to me ? Thanks. Brandman.

 

[gigem75]

Ed, I think that's a great idea. There does seem to be some confusion as to what is and isn't a emmision weber. I'm pretty much in a constant state of confusion as can be deduced from many of my comments such as when in earlier posts the 151 seemed to be considered an emmision weber when in reality it merely has a later style idle circuit. Also it appeared to me anyway from other statements all webers made in Spain were considered emmision webers even though they are manufactured to ISO 9000 specs from previous models. Bottom line any information to clear up whats what would be greatly appreciated.

 

[alfaparticle]

Or some of them don´t have a pump back bleed. (106/107 , 130/131, 138/139, .

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.

do all of them need the short version of the accelerator pump jet ?

I cannot find any references to different length pump jets.

By the way: i am looking for 0.30 Pump jets ,the short version. But it´s difficult to get them in europe. Does anybody sell them to me ?

I buy my jets from Alfa1750 on ebay. He is in Italy. He knows emission DCOE's.

 

[Brandman]

Thanks for contact, i´ll try it.
In the exploded view for DCOE138/139 you can see the short version of the pump jet.
A big dealer in UK told me, it doesn´t matter if i would use the long version. The guys from VGS (germany) told me that the short version is requiered, a must have.
(I don´t know why, but i can´t attach any files here)

 

[Gasolina]

Here's 138/139 in details;

 

[alfaparticle]

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.

 

[Gasolina]

Hi Ed,

Those are specsed for 016.55 engine Alfetta GTV. Another variation for the same car seem to be 124/125 See the attachment.

 

[gigem75]

Got the 32 chokes today and they're in, test drive tomorrow morning. I did a compression check before and will do an "after" as well. Should be interesting.