Part Identification Assistance for Weber 34ADF

[howelljd]

I need help obtaining a replacement part for my Weber 34ADF carburetor. I was fortunate to locate a used Weber 34ADF online for a great price. I had to drill out the bolt holding the water activated choke mechanism but I successfully installed a heli-coil to repair this issue. I cleaned it up and replaced the gaskets, O-rings, pull-off choke diaphragm, accelerator pump diaphragm, auxiliary pump diaphragm, and idle solenoid but there is a damaged part that I need to replace and I am unable to identify the part:

This appears to be an air mixture adjustment screw but it is buried in the throttle body under the carburetor body:

It appears to meter air through the secondary venturi above the throttle plate and via the manifold:

This screw is M5-0.8 x 9mm threaded with a 3mm diameter x 5mm long barrel that then tapers to a point over the next 7mm.

Thanks for any help identifying this part or providing a suggestion on how to proceed.

Cheers,
Jonathan

PS: I updated the measurements as I made an error earlier. The barrel of the screw is 3mm not 3.5mm.

[howelljd]

I was able to get a machinist to fabricate a replacement for this part. I've re-installed it in the throttle body by seating it and then backing off 1-1/2 turns as this seems to be a good starting point for air screws. Of course, since this screw is not an easily adjustable item, I remain interested if any others have encountered such a screw in other Weber 34 ADF 54 250 2M carburetors. I will be using this 34 ADF with a Computronix EDIS.

Hope to hear any feedback!

Cheers,
Jonathan

[Nanonevol]

Well, that's interesting. I'm studying my 34ADF and mine lacks that's feature. I see other differences too.

[howelljd]

I do find it interesting! The thought had previously crossed my mind that perhaps there were various throttle assemblies that could be swapped but I haven't found any documentation to support this theory. The differences for manifold vacuum are easily visible. There are also pathway differences and the unusual "L-shaped" block in my throttle assembly. My 34ADF came from a Fiat 131 based in Europe. Thanks for your note and photo for comparison!

Cheers,
Jonathan

[msjulian]

Just so happen to have mine apart for a rebuild...



Mine has the brass screw but it appears to not be adjustable as I am unable to unscrew it from the base. Not real sure what it does.

[Nanonevol]

Here's the side with the stamp on mine. These are amazing contraptions.

[howelljd]

@msjulian - do you have any history on the source for your 34ADF? That brass screw is not an easily replaced item so I encourage you to leave it alone. I was able to extract the screw - obviously with sufficient force - but when it started to come out of the throttle assembly I did not support the split barrel (an M5-0.8 nut would have done this very well) and the sides were deformed as a result. Could you get a measure of the distance from the top of the screw to the top of the throttle assembly with a micrometer possibly? That would help me to determine whether 1-1/2 turns out is sufficient.

These carbs are awesome!

Cheers,
Jonathan

[msjulian]

I purchased it from a gent in Australia about 14 years ago. Can't remember what he told me it came off of. I can get a measurement for you this weekend.

[howelljd]

Any chance you were able to get a measurement of how far the top of the screw is set below the top of the throttle assembly? Thanks for any help!

Cheers,
Jonathan

[131]

I purchased it from a gent in Australia about 14 years ago. Can't remember what he told me it came off of.

If it's from Australia it's probably from a 2l 131.

[msjulian]

I should be able to get that for you tonight.

[seabeelt]

IF you folks go to: piercemanifolds.com, they have on line diagrams and parts for each weber carb, or can get them

[msjulian]

NO 34ADF diagram on Pierce Manifolds...

Mine is .0410 deep

[msjulian]

NO 34ADF diagram on Pierce Manifolds...

Mine is .0410 deep

[howelljd]

I have ordered many parts from Pierce Manifolds and while their diagrams are useful, the part I requested assistance with has eluded formal identification. I greatly appreciate the measurement to get a reasonable starting point with my custom replacement part.

Cheers,
Jonathan