The Lost Art And Black Magic Of Weber Sidedraft Carbs

[gav240z]

I thought a few here might appreciate the read here.

http://www.roadandtrack.com/car-culture/a25816/lost-art-the-weber-sidedraft-carburetor/

[AndBir]

This seems a good reference : http://240260280.com/Tech/Carbs/Weber/DCOE Theory Operation and Tuning.html

[gav240z]

That's a really good resource.

[AndBir]

On 5/30/2019 at 5:03 PM, gav240z said:

That's a really good resource.

From the copious amount of reading I have done it appears one of the most critical initial aspects to get correct idle settings is to ensure the throttle plate is positioned such that it is in front (ie covering) of the first progression hole - easier to do with the DCOE152G (4 hole) carbs.

Most discussion mentions "adjusting the idle speed screw ¼ to ½ turn in after contact with lever" - I am unsure if this results in the throttle plate being positioned correctly wrt the first progression hole or not.

Interested to hear how owners here have completed their initial set up of their triple dcoe webers?

 

Throttle plate position at idle setting

Edit : Seems that the Weber Tuning Manual outlines the correct throttle plate position which is shown as A below.

B will result in a flat spot on initial acceleration

C will result in a rough idle not resolved by changing the idle mixture screw position.

 

Edited August 18, 2020 by AndBir
corrected terminology

[krizza]

If the carbs are off the manifold it is easy to set the butterflies by inspecting their location in relation to the first progression hole when viewed from inside.

If they are already installed on the car you remove the inspection plugs and use a torch to view the location of the edge of the butterfly in relation to the first progression hole. Once you have read all the literature a few times and then go over the carbs you get a feel for it. Either way it is something you need to do by eye. 

One of these style carb synchronisers is essential to get them balanced and a good investment -    

[AndBir]

8 minutes ago, krizza said:

Once you have read all the literature a few times

That seems to be the problem, as there are differing views on doing an adjustment of the idle speed screw after adjustment of the idle mixture screws which would result in the throttle valve moving off the 1st progression hole.

I did invest in that synchroniser, can't imagine how you could balance the carbs otherwise although you do see some "interesting" methods on the odd YouTube video.

[AndBir]

Other than not directly referencing the position of the throttle plate at idle this seems the most complete DCOE reference : https://240260280.com/Tech/Carbs/Weber/docs/Hammil/Power Tuning Webers V1 (text search).pdf

[AndBir]

On 8/14/2020 at 9:44 PM, krizza said:

Once you have read all the literature a few times

OK, I have spent too long reading and realise that the literature out there covers many generations of Weber DCOE carbs and as such you need to be careful interpreting what is relevant to the model of Weber DCOE carb you have.

I expect most people with 45mm Webers will have either the 152 or more recent 152G DCOE models (made in Spain)so if looking to get the idle "tuned" on these then as a starter :

1) Adjust your tappet clearances.

2) Adjust your idle timing to reflect what cam you have 10 btdc for stock, 12-14 BTDC for mild cams etc.

3) i) For the 152 model you will likely need to drill an additional progression hole as per this post : 

3) ii) For the 152G models, ignore the literature that references adjusting the idle speed screw by 1/4 or 1/2 etc. turns - just ensure the throttle plate edge is aligned so that it covers the first progression hole as shown in this video : 

You can then move onto adjusting the idle mixture screws as per the methods in the literature and then moving onto changing your jets emulsion tubes etc. to suit your engine and type of driving.