Alfa Romeo Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
41 Posts
Discussion Starter #1
Hello Everyone,

I have two Weber 40DCOE27s that were given as spare parts for my father's Duetto many years ago. They are different from each other and the book I have does not describe one of them.

On the Weber on the left:
What are the white caps on the left and right side? They don't come off easily and I don't want to force them off until I know what they are.

There is an extra adjustment screw between the idle mixture adjustment and the progression cover. I have seen some Webers where there is a place in the casting for this, but its not used. That place is completely missing on the weber on the right.

Left Weber No 15646
Right Weber No 17135
Of course, who knows what carb the cover plate originally fit to.

Carbs are a new toy for me. I am a little more familiar with diesel injection pumps right now.

Thanks!
Arne
 

Attachments

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
I would say that the left carb is a later, emission carb. Like a 130, 150 or a 170 series perhaps. Someone simply put a type 27 cover on it. I would not pair it with the carb on the right; best to find another type 27.
 

·
Premium Member
Joined
·
13,694 Posts
I agrre with Jim that it is an emissions carb, but I don't know which one. I have 40DCOE116/117 on my Spider and 40DCOE138/139 on my GTV and they don't have the white plastic things.
Ed Prytherch
 

·
Premium Member
Joined
·
582 Posts
Couldn't he at least use the main casting and just swap out the Venturi and all jets to meet the other carb's specification? If not, what is different? I know the main casting is different between the 40 and 45's, but I am not sure going down the scale. A '40 DCOE32' will only accept a Venturi as large as 36mm, making it a '40DCOE36' (and then you would want to change the main and idle jets accordingly). Regardless of my data, he might only have to change internals to match the other carb's through put....
 

Attachments

·
Premium Member
Joined
·
13,694 Posts
There are differences in the carb body. The idle circuit in the emissions carbs is supplied from the well whereas it is supplied from the float chamber in the classic carbs. Also, the emissions carbs have different progression holes.
I have a 40DCOE32 less venturis and jets that is doing me no good. I will sell it for a modest fee. It may be compatible with a 40DCOE27.
Ed Prytherch
 

·
Registered
Joined
·
41 Posts
Discussion Starter #6
Thanks for the info, guys. The old car has two supposedly good, identical carbs on it. I just have not started taking things apart. I hope that they are non-emissions types.

The book "How to Build and Power Tune Weber and Dellorto Carburettors" by Des Hammill says that the number of progression holes is a good giveaway for an emissions carb. Both have just three holes. But maybe that was changed somehow.

Thanks for your help!
Arne
 

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
A '40 DCOE32' will only accept a Venturi as large as 36mm, making it a '40DCOE36'...
While a 36mm venturi will fit a 40 DCOE 32, this does not then make the carb a 40 DCOE 36. The last two (sometimes three) digits refer to a specific venturi/jet size combination and has nothing to do with venturi diameter. The DCOE 32 is the only (Alfa) DCOE that I know of where the type number coincidentally matches the venturi diameter.

Some DCOE Alfa fitments are listed here.
 

·
Premium Member
Joined
·
582 Posts
Thanks for the correction Papajam...I was making an assumption. Notice that when you buy a DCOE carburator, it now references a 3 digit number (e.g. 40DCOE151). What I do know is that a '40' DCOE will only accept a primary Venturi up to 36mm.
With a stage 3 prepared 1750 cylider head, is there going to be a need or added benefit to increasing any combination of the jets/venturis over the stock 40DCOE32 set-up? Asking the question here and will do a search through the BB and Web...
 

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
Yes, there would be a benefit to changing venturis/jets. Alfa chose the 32mm venturis for the 1750 and 2000 to provide all around tractability in all rpm ranges. Generally, smaller vents provide for better drivability at lower rpm but restrict airflow at high rpm. Larger vents are the opposite; provide more airflow at higher rpm while sacrificing lower rpm drivability. The key is to find the right balance between your engine mods, how (and where) the car will be driven and your driving style.
Please give this article a read and we'll go from there.
 

·
Registered
Joined
·
41 Posts
Discussion Starter #10
So I've finally got the carbs off the Duetto and they are not identical. They have slightly different castings, but neither are emissions carbs. One claims to be 40DCOE44 and the other 40DCOE2, but again, who knows what is true. The casting of the DCOE44 is identical as far as I can tell to the right one in the original post.

So, my question is this. For similar castings, the only thing that can be different are the progression holes, right? Are these holes as precisely drilled as the metered orifices in the jets? The two castings seem to be the same, by eyeball, but I have no way to measure for sure.

Thanks,
Arne
 
1 - 10 of 10 Posts
Top