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Weber 34 ADM carb conversion info


1963 AP5

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Here is some info on the Weber 34 ADM carb as found on the XE/XF Falcon. This was a popular carb for retrofitting onto other vehicles but they are have a couple of little quirks that can  cause problems if you are not aware of them.

Firstly there is the 2 stage low speed jet solenoid. This was an emissions control system that allowed the engine to run with one jet size when cold (think it was a 70) and when the engine warmed up it switched to a smaller jet to reduce emissions (possibly a 55). Problem is they get old and the little diaphragm inside fails allowing fuel to flow from the primary low speed circuit through the failed solenoid and into the line that supplies vacuum to the system. this causes the engine to run super rich. But don't worry there is a solution. 

The products that solve the problem can be found here.

https://www.weberperformance.com.au/product_info.php?cPath=6_268&products_id=631

https://www.weberperformance.com.au/product_info.php?cPath=6_268&products_id=1345

This is a larger jet holder that deletes the solenoid and the appropriate jets to go with it. You will need to mess around with the jets to find the right one for your engine. I think I ended up with a 60 or 65 in mine.

Here is a picture of the system on the standard carb and another of the carb on my car with the system deleted.

You will note that all the vacuum ports except the vacuum advance are simply capped off because all the emissions control stuff is gone (EGR etc).

 

Vac line pic.jpg

20200710_110756.jpg

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Second trap is the one that catches most people out.

The vacuum port for the power valve is in an odd place on these carbs and some off the shelf adaptor plates will blank it off causing the engine to run on the power valve all the time and run very rich. The port is actually under the base plate and is not open to either of the carb barrels.

The common adaptor plate available for a Holden 6 is a redline product designed for a 23/36 weber and there are a few problems with it when using a 34 ADM. The first one is it too low and the accelerator pump lever hits the adaptor. Secondly the barrels on a Weber 34 will not align with the adaptor. I chose to make an additional spacer to adapt the carb to the adaptor. Yes I know it seems silly to make and adaptor for the adaptor but it worked and solved both problems. 

You need to drill a vacuum port for the power valve in the adaptor plate and this port needs to also be drilled all the way through the stock manifold. If this port is omitted, vacuum will not be supplied to the power valve or the accelerator pump boost diaphragm and the carb simply wont work properly.

If you look at the underside of the carb you will find the port (it might even be blocked with crud). The port is located between the primary and secondary bores and continues up through base and into a tube in the carb body. The tube also acts as a locating dowel and can sometimes become damaged and obstructed if the carb hasn't been assembled correctly at some stage in the past.

Useful info on this can be found here

http://www.mbs.id.au/tuning/Carburettors/Weber/34ADM.htm

I wish I had documented this part of the process better and taken photos but I will try to show this with pics from the internet. 

ADM_carb.jpg

Exploded carb.jpg

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This may be useful to you to as well it shows the correct jets for the carb in stock form and this is exactly what I run in my car. These carbs are getting old and often people have messed around with them, changed jets for a particular application or drilled the jets. You can get tools for measuring the jets to ensure the orifice is the correct size, they are cheap and a very good investment.

ADM carb jetting picture.jpg

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One more pic showing the other side of the carb. I have the throttle nudger blanked off on my carb, I think this is supposed to hold the throttle slightly open momentarily if the throttle is snapped shut suddenly to smooth things out. On some models it may also have been supplied vacuum as an idle up system for air con etc. The diaphragm can fail and cause a vacuum leak and most of the carb rebuild kits don't include this particular diaphragm. You don't need it so I just capped the rather large vacuum port.

Alt view.jpg

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  • 2 years later...
On 22/07/2020 at 07:39, 1963 AP5 said:

The vacuum port for the power valve is in an odd place on these carbs and some off the shelf adaptor plates will blank it off causing the engine to run on the power valve all the time and run very rich. The port is actually under the base plate and is not open to either of the carb barrels.

further down
You need to drill a vacuum port for the power valve in the adaptor plate and this port needs to also be drilled all the way through the stock manifold. If this port is omitted, vacuum will not be supplied to the power valve or the accelerator pump boost diaphragm and the carb simply wont work properly.

BUGGER ME! 

i had just been reading your awesome thread (second link in first post no longer works, any idea what it was for?) 

anyway, i had tried(failed) one of these carbys on my gemini 2litre (rodeo engine) briefly and it was running rich to the point of fouling the plugs and sounding like a PP rotary  
i'll bet it had the vacuum port blocked due to the adaptor plate for the 32/36

My first thoughts were this carby was HEAPS more responsive than the 32/36 i ended up with (dyno tuners choice, he said they'd flow similar, and the smaller primary on the 32/36 would better suit the 2 litre..)

i had started trying to remove the power valve(interference fit) and gave up.. bought another carby but was persuaded to go to the 32/36 by the tuner. (lucky i didn't try fit the second 34ADM as it would have done the same. 

Brilliant thread @1963 AP5 I'm glad you took the time to document it and explain it so well. (i'm expecting that carb to be fine albeit with plier marks all over the power valve boss :(  ) 

 

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On 08/03/2023 at 14:53, deankdx said:

BUGGER ME! 

i had just been reading your awesome thread (second link in first post no longer works, any idea what it was for?) 

anyway, i had tried(failed) one of these carbys on my gemini 2litre (rodeo engine) briefly and it was running rich to the point of fouling the plugs and sounding like a PP rotary  
i'll bet it had the vacuum port blocked due to the adaptor plate for the 32/36

My first thoughts were this carby was HEAPS more responsive than the 32/36 i ended up with (dyno tuners choice, he said they'd flow similar, and the smaller primary on the 32/36 would better suit the 2 litre..)

i had started trying to remove the power valve(interference fit) and gave up.. bought another carby but was persuaded to go to the 32/36 by the tuner. (lucky i didn't try fit the second 34ADM as it would have done the same. 

Brilliant thread @1963 AP5 I'm glad you took the time to document it and explain it so well. (i'm expecting that carb to be fine albeit with plier marks all over the power valve boss :(  ) 

 

Thanks for your kind words.

The second link was for a special large jet holder that fits in place of the original 2 stage low speed jet solenoid assembly. They used to be available off the shelf but maybe there isn't enough demand anymore to keep making/selling them. It is possible to make a suitable jet holder if you measure up carefully and have acess to a lathe.

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1 hour ago, 1963 AP5 said:

Thanks for your kind words.

The second link was for a special large jet holder that fits in place of the original 2 stage low speed jet solenoid assembly. They used to be available off the shelf but maybe there isn't enough demand anymore to keep making/selling them. It is possible to make a suitable jet holder if you measure up carefully and have acess to a lathe.

thanks for the info, i thought it must be the jet holder as it was the only thing i didn't see in the pics of the first link. 

i didn't know this was a switched jet (temp switch) as the later ones don't have it, or if they do it's not via that vacuum switch (I had XE XFs for 20yrs  until about 10yrs ago) 

I am now understanding why the tuner preferred the 32/36,  had heard of them fitted to the falcons even and probably go well, the bigger 38/38 is also a direct fit but both barrels open together. 

due to my feeling that the 34ADM (falcon carb) was more responsive on my gemini, i'm still tempted to fit one if i do any changes that would need rejetting. so this info is extremely helpful (probably so i can TEACH the tuner also) 

weber performance have been really good at replying to emails, so i'll ask about that jet holder and see if it's still available and if so reply back with info.

lastly, do you have a review on fuel economy/drivability on your engine? on the 250ci falcon XE XF i used to be able to get 10L per 100km with them at 2300rpm for 100khm long drives. 

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  • 2 weeks later...

You are correct, not all 34ADM's have the 2-stage jet, only the ones that were equipped with emission control gear.

The 34ADM has a very large secondary venturi and I think that is why it uses a very large secondary jet. Some small engines struggle with the Weber 34 because they simply can’t get enough airflow through the secondary venturi to make it work properly. For this reason, the 32/36 is often a better option for engines under 3.0L. I believe the secondary venturi is actually smaller on a 32/36.

I have never actually worked out the fuel economy on the Holden, but I expect it is similar to the original Rochester carb (certainly no worse). I think the Weber is more responsive than the original carb but to be fair the original wasn’t working properly and that’s why I replaced it with the Weber. I simply couldn’t get a kit to overhaul the original carb so the Weber conversion was a good option. It’s been running trouble free with the Weber on for around 5 years now.

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13 hours ago, 1963 AP5 said:

I believe the secondary venturi is actually smaller on a 32/36.

I'm not sure about the venturi sizes, only the butterflies are pretty much as the carb identifies 34ADM both 34mm and 32/36 one is 32mm and the other 36mm(which My tuner said along the lines of much a muchness, basically will flow the same, but the primary being smaller will suit the smaller engine due to better air speed. *(I've been told the bigger 2 litre Nikki carb on the rodeo 2 litre would go about the same on Mine, but better on fuel than the weber due to vac secondary, but they were all worn out 30yrs ago and in the bin) 
I never got a reply from Weber Performance regarding the jet holder either.

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Looks like the large jet holder is still available overseas

Primary Idle Jet Holder for Weber 32/36 DGAV, Large Size - Pegasus Auto Racing Supplies

52570.011 - Jet Holder LARGE fits Weber 32/36 DGEV DGV DGAV DFEV DGES (carburetion.com)

and Weber Performance in Australia still sell the larger jets to suit the 34ADM.

DGAV DGAS ADM Weber Carburettor Idle Jet (larger primary) Weber Performance Carburettors

Have a look down the carb barrels on a 34ADM, you will notice that even though both have 34mm butterflies the venturi sizes are very different between the primary and secondary. Insufficient air velocity through that big secondary venturi can be a problem on small engines unless they are fairly heavily modified and screaming. The carb is really designed for larger capacity engines (4.1L Falcon) but was a popular swap for modified engines with smaller displacement simply because they were cheap and plentiful back in the day. Mine works great on a 3.3L Holden 6. I have never tried one on anything smaller but I have heard of people having success with them on modified 4 cylinder engines.

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  • 9 months later...

Hi Guys I've been reading 1963 AP5 about the 34ADm Weber's and very informative. I've been making a manifold for my 4.1 crossflow for triple 34ADm Weber's bit of a challenge but done. Recently installed on to my Cortina 1981 TF and after reading some of the informative info trying to understand the operation of the carb read the Yellow Ford technical Bulletin and still having trouble after isolating the vacuum switch for idle jet found one has a ruptured diaphragm so plugged it up and the vacuum connection for the nudger diaphragm as you have done and shown in the pic's and still running extremely rich. Has a healthy cam and when I disconnected the 12vdc solenoid above the adaptor plate indicated in your picture, seams to settled down to normal not choking with carbon. Can some one tell me what the solenoid's function is, I'm thinking it could be some kind of valve for idle function.  Look forward to any feed back would be much appreciated. Wish every one a great new year. Peter Sav. 

                   

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On 20/01/2024 at 17:37, TF cor said:

Hi Guys I've been reading 1963 AP5 about the 34ADm Weber's and very informative. I've been making a manifold for my 4.1 crossflow for triple 34ADm Weber's bit of a challenge but done. Recently installed on to my Cortina 1981 TF and after reading some of the informative info trying to understand the operation of the carb read the Yellow Ford technical Bulletin and still having trouble after isolating the vacuum switch for idle jet found one has a ruptured diaphragm so plugged it up and the vacuum connection for the nudger diaphragm as you have done and shown in the pic's and still running extremely rich. Has a healthy cam and when I disconnected the 12vdc solenoid above the adaptor plate indicated in your picture, seams to settled down to normal not choking with carbon. Can some one tell me what the solenoid's function is, I'm thinking it could be some kind of valve for idle function.  Look forward to any feed back would be much appreciated. Wish every one a great new year. Peter Sav. 

                   

 

that's a fuel cut solenoid, stops run on when ignition is turned off. 

 

I saw this photo many years ago, i think it was mentioned it was 3 manifolds cut up and bolted on separately 
xLEbmyY.jpg

 

 

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