MatraSport Forum

General Matra related => Anders Dinsen's Weber Blog => Topic started by: Anders Dinsen on August 08, 2008, 04:37:20 pm

Title: Early thoughts
Post by: Anders Dinsen on August 08, 2008, 04:37:20 pm
The carburettors is a matched pair of 40 DCOE 31's. The 40 designates the size of the bore (40 mm) and the 31 is a type number. The Weber DCOE carburettor is a legendary piece of mechanics with roots in the sand cast DCO carburettors which Eduardo Weber developed in the early 50's. The E means that the body is die cast, but otherwise they are very similar to the DCO's.

The 40 DCOE 31 was used on the Lotus Cortina in the 1960's, and my carbs could be from one of them, but could also come from another car. I don't know how old they are.

They were bought by Matra-Hans from Simon more than 10 years ago along with a reproduced S-manifold, the necessary extension to the thermostat housing, a pair of K&N pancake filters, and ready jetted for an S-cam. Carbs were used, K&N filters seem used too (but the filter elements look new), and the manifold is new. They were probably more or less ready to be fitted to the car. Hans never used them, though, and since he is down another road now (turbo!), he offered them to me ans I took them over from him in mid July, with no specific plan as to when or how to fit them.


There's a special atmosphere surrounding a pair of sidedraughts like this, and it comes from the racing heritage they have. They were more or less the ultimate setup on race cars through the late 60's and well up into 80's. They are rugged, easy to maintain, and jets and venturis can be easily changed on-track with the carbs still on the car.

This is the configuration they have:

Venturi: 36 mm
Aux: 5
Idle jet: 45F8
Main jet: 150
Emulsion tube: F9
Air corrector: 180
Acceleration jet: 35

Since the above photo was taken, I have sold the Magard linkage to a Cortina owner in Norway, who wanted something that looked original on his car, and has ordered a new Weber linkage and two sets of gaskets. I have also repaired the starting mechanisms (one had a lug broken off), and I've had both carburettors more or less dismantled and checked. They look good and just need the new set of gaskets.

Test fitting the carbs. The water channel extension is necessary to clear the thermostat housing from the carbs.

The first progression hole of the 40 DCOE 31 is located very far ahead being uncovered as soon as the throttle plate starts moving. Idle is therefore more or less unadjustable by the idle speed screw on the side of the carb as moving the throttle plate by just a little bit will uncover this hole and make the mixture far too rich. Instead there's a 1 mm hole drilled in the throttle plates. If the idle speed is not high enough, these will have to be drilled out to 1.5 mm.

I have more photos on my own gallery, here:

Title: Re: Early thoughts
Post by: Spyros on August 10, 2008, 12:19:22 pm
I see that on this engine, you have a separated manifold for the thermostat.
I'll need to build something like that for my golf 16V adaptations on the Simca engine.
Is it possibe to have more pictures of the details ?


Title: Re: Early thoughts
Post by: Anders Dinsen on August 10, 2008, 01:01:19 pm
Sure, Spyros - I'll PM you when I have taken some pic's of the extension. This is a standard feature of the Murena S, BTW.
Golf 16V adapted to what? I hope you'll tell us more in your blog :D

Title: Re: Early thoughts
Post by: Spyros on August 10, 2008, 06:05:10 pm
Old project, see here (
Yes, I know, it's in French. Sorry for that.

I'm currently with 2 half cooked engines,
One with injection, to which I'm thinking to add something to the exhaust ...

And the second with a pair of Dellortos (cheaper than your DCOE'S)