Lancia Beta Forum

Technical stuff => Fuel System Carb => Topic started by: Alastair Watson on January 26, 2024, 12:16:41 PM

Title: Weber 34 DATA
Post by: Alastair Watson on January 26, 2024, 12:16:41 PM
Hello and thank you for admitting me to your forum.

It was the only place that I could find any reference to a Weber 34 DATA at all.

At this point, I should confess that the carby is not currently gracing a Lancia but is instead fitted to my 1976 Fiat 128 3P, running a 1.3 litre engine w/ a port-matched and polished inlet manifold, a mild cam, electronic ignition and extractors. 

I hope this is ok w/ you. 

Iíve done a rough job rejetting the carby, based on info on the X-Web for a car w/ similar specs. 

Itís not perfect but itís running ok.

I also went to adjust the idle mixture but canít see where the screw is - it doesnít seem to be in the same place as it is on the 32 DMTR that was on the car. 

The equivalent spot of the DATA seems to be a shallow and blind hole, without any thread, which is why I donít think the screwís meant to go there.

Is anyone able to point me in the right direction, please?


Tasmania, Australia.

Title: Re: Weber 34 DATA
Post by: HFStuart on January 26, 2024, 01:54:39 PM
I think we'll allow a cousin to join in! Especially as a decent proportion on here will read 3P and think 'oooh, nice!'

Looking down on the carb the idle mixture screw should be roughly as indicated by the arrow in the side of the carb body  - almost in the baseplate.  I say should as there are a LOT of variants on the DATR / DMTR. A couple of photos of the carb from either side with the air cleaner off would help.

     ¶      ¶
     ¶      ¶
     ¶      ¶
     ¶      ¶
     ------    <-----
   /   ¶  ¶  \
 Inlet manifold

Title: Re: Weber 34 DATA
Post by: smithymc on January 26, 2024, 02:26:30 PM
Another 3P fan here.


Title: Re: Weber 34 DATA
Post by: Nigel on January 26, 2024, 10:20:46 PM
Hi all,
Referring to Stuarts drawing, on my 34 DATR the mixture screw is opposite
to the marked arrow, but as said, many variations exist.


Title: Re: Weber 34 DATA
Post by: Alastair Watson on January 27, 2024, 06:42:10 AM
Thanks, HFStuart, Mark and Nigel.

I had been looking for the screw on the baseplate on the opposite side to the inlet manifold (the back) rather than the left and right sides.

Itís hissing down here at the minute (not an ideal summerís day!) but Iíll be checking out both suggested locations when itís dry again.

Iíll try to get photos, too.

Will update with outcome.

Assistance much appreciated!



Title: Re: Weber 34 DATA
Post by: Nigel on January 27, 2024, 09:24:27 PM
Hi Alistair,

I've now dug out my Aussie carb and hopefully these photos will
It is possible that this location is capped with
an alloy plug. This was a factory action to prevent tampering with the
emissions settings but they are normally long gone.

Title: Re: Weber 34 DATA
Post by: Alastair Watson on January 29, 2024, 01:54:47 AM
Thanks, very, very much, Nigel!  Thatís extremely helpful.  Yours is the exact same model as I have.  Mine is capped.  I think thatís all I need to know now.  I canít imagine that itís super difficult to uncap the hole.  However, I think it puts the job into the specialistsí sphere, as thereís too much mucking about for me to do it:  uncapping, knowing which screw to use, sourcing parts, etc Ö .   The carby needs to be rejetted anyway, so Iíll get it done professionally.  (http://)

Title: Re: Weber 34 DATA
Post by: JohnFol on January 29, 2024, 03:39:06 PM

Big fan of getting them adjusted by someone who knows what they are doing but if you know the jet sizes, it's a very easy job and cheap. I got mine (plus emulsion tubes / air correctors ) from these people (

Swapping them over is measured in minutes not hours

Title: Re: Weber 34 DATA
Post by: Nigel on January 29, 2024, 10:43:18 PM
Hi Alistair,
There will be an adjusting screw behind the plug if
you're feeling adventurous. The plug will come out with a
sharp-pointed thing, it's quite soft.


Title: Re: Weber 34 DATA
Post by: Alastair Watson on January 29, 2024, 11:20:17 PM
Thanks, John.

The physical swapping isnít what scares me; itís knowing whatís likely to work on my slightly modded 1.3 Fiat v the way itís set up for a 1.8 or 2.0 Lancia.  I got it going reasonably well using jets, emulsion tubes and correctors I already had, based on info from an X1/9 forum, but now itís specialist time, especially seeing the mixture screwís been ďhidden.Ē

Title: Re: Weber 34 DATA
Post by: Alastair Watson on January 29, 2024, 11:28:41 PM
Hi, Nigel.

Iím sure youíre correct but I think itís pro-time so that the carby can be ďpersonalisedĒ to the car itís on. 

I was going to have a crack at the mixture if I could find it (get it running a bit smoother / learn something).

Too many variables now - jets, e tubes, correctors - for an amateur like me, Iím afraid. 

Thanks again for your help.


Title: Re: Weber 34 DATA
Post by: Alastair Watson on May 24, 2024, 12:12:55 PM
Hello, all, especially Nigel, John and HFStuart, and your moderator / admin person who kindly admitted me to your forum. 

I finally had my DATA 34 jetted and tuned and now itís working a treat. 

Both the idles and primaries were replaced with bigger items, as suits my particular cam profile etc.

If anyone needs to know the exact specs, please email me on (I wonít post them here, seeing itís a Lancia forum and my 128ís specs are fairly individual). 

The big one for me - the main reason I sought your collective advice - was to locate the missing-in-action mixture screw, which the Weber specialist mechanic showed me on the passenger side* of the carby, at the rear.   It wasnít capped; the screw was just well hidden. 

The location is probably best shown in the attached photos, with the screw having been indicated in the close pic with the pointer.

I hope this may be of assistance to someone, at sometime, on this forum.

Thanks again for your generous assistance.



*Iím Australian; we drive on the same side of the road as you do in the UK.