I finally finished the Zenith to Weber conversion on my 69' 108.

Due to ongoing issues with my Zenith carbs I decided to do the swap. The C-501 Weber kit was purchased from JAM engineering and arrived at my door in a few days. Since my car is a pre 70' I did not need to get the Idle shut off solenoids, there is no wiring for them anyway on my car.

I followed this post from OZBENZ for the most part...OZBENZ - Australian & New Zealand Mercedes-Benz Forums • View topic - Dave's Weber Carby Conversion 'How To' Thread - W111/108/114
This is a great write up with good info and pointers!

Here is my observations during the install...

To start off with...
The fuel inlets need to be swapped on both carbs. That way the fuel line is not directly over the manifold.

The linkages supplied for the carb to throttle swing arm is indeed too short but they are metal. When the carb is extended to full throttle the supplied linkage gets bound up and throttle sticks to full WOT. I needed to extend the linkages as listed in the OZBENZ thread to prevent this. The guy started with about 80mm, that was too long for me so I am around 70-60mm which gives nice travel and no bindage

BOTH brackets for the throttle swing arms do need to be ground down abit as they do hit the manifold...
(Image borrowed from OZBENZ)


After that I could test fit the carbs...
Right away I noticed that the exhaust emission control plumbing was in the way.


Screw it, I chopped the emissions air return tube off. I was not able to locate a correct plug for the port so I just hacked off the tube and pinched it with a hammer to make it air tight. Not the best way but it will work for now. The other end has been done in the same manner.

because of the manifold and the way the carb is manufactured I needed to hack almost 5mm off of one of the mounting bolts for the front carb, (driver side front bolt). The bolt was just too long to go up through or down through. An easy fix and still had plenty of thread to secure it down.

Carbs installed...
This part was straight forward


After some trial and error I got the swing arm linkages adjusted and set correctly so the carbs wouldn't stick open at full throttle.
Gas lines plumbed...


Before I tackled the transmission downshift issue I fired it up. I must say that my car is very happy with the Webers directly out of the box. I hadn't touched anything and idle was smooth and throttle response was quick.

Since I knew it wouldn't explode and the carbs were working correctly I could move along to the transmission "soft downshift switch". I bought a 2 prong microswitch from JEGS online which had a bendable mount that really came in handy.
I removed the wires from the Zenith actuator and connected them to the microswitch. It took a good hour of positioning and re-positioning it to find a good spot. Here is where it ended up, on the rear carb...




Once I had it bent and torqued down, I double checked the switch action. Everything was connecting and switching correctly so it was time to drive.

I was a bit skeptical about it but low and behold it works! The down shifts and even upshifts are smooth as butter. Feels like a newer automatic car in terms of shifting.


When it came time to refit the stock air box there was a problem. The JAM towers are too tall for the airbox to mount flush to the carbs. They are about 1/4in too tall which sucks...


I guess I will need to dish out another $40 for the Weber DGEV carb air boxes.


All and all I am pretty happy with the kit and glad the microswitch worked out. With some fine tuning of the carbs it will be that much better.
I am sure I am leaving some things out so I will update this as needed.

I do have a fuel pressure regulator ready to put in but I haven't yet. I think my fuel pump screen is partially clogged so gas isn't flooding the Webers for the time being. Until I clean it out I should be fine.
The fuel return line has been blocked off as well.

Let me know if you have questions or anything!

-Nate

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1969 w108 280s

You're beautiful, man. Finally, answers to the age-old questions about Webers.

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1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"

Thanks man
The info was out there so I just put it all together with pictures!

__________________
1969 w108 280s

Update to this...

I couldn't use the stock airbox/breather hose setup from the crankcase due to the JAM towers being too high so I needed to find a breather filter that fit.
Heres the link to that thread...

http://www.peachparts.com/shopforum/vintage-mercedes/364237-w108-crankcase-breather-filter.html

Enjoy!

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1969 w108 280s

Interesting, I used the exact same little microswitch for my trans solenoid. Funny little world. On my car I could never get it to reliably close every single time and so had the occasional rough downshift while slowing down to a stop. My transmission was a brand spanking new one straight from M-B so I really didn't want to drive like that for too long.

The other problem I had was hot starting in the heat of summer. I always had to floor it and clear the carbs while cranking quite a bit after a heat soak. I believe the fact that the weber kit has no provision for a fuel return exacerbated the problem. I do remember the webers running really nice and smooth "out of the box" just like yours. I recommend running the fuel lines on the opposite side of the carbs away from the engine if you haven't already. There is a provision to mount the fuel hose either way on the carb. Perhaps you won't run into that issue anyway...

It was a really nice feeling to install the carbs and have them running so smoothly so quickly though, good satisfaction.

Cheers,

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1967 230S automatic
Boston, MA

Hi,

You can buy these spacers that sit inbetween the manifold and under each carb which makes the carbs sit higher.

You just need to kind of make a sandwich of them: Carb/gasket/spacer/gasket/spacer/gasket/manifold

In my 72 they (prior owners) used the two air boxes you're talking about, but in my 71 they used the technique i described above.

I like the look of my 71 better (once air filter is on top, don't even notice they are modified webers; looks 100% original). Using two air boxes allows you better access to fine tuning the carbs without having to pull off a bunch of tubes, but the thing I hate the most is the breather hose then has to be re-routed below the engine (so your car engine bay smells of exhaust fumes which you can smell inside car vs. it all going out exaust waaaay in back of car).

Jub

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Current:
1971 Mercedes Benz 250 (Euro Spec)
1972 Mercedes Benz 250 (US Spec)
Past:
1972 Mercedes Benz 280

Heres one for fiats (just quickly googled it):

FIAT 124/131 CARBURETOR SPACER, WEBER For Sale - DVAutoParts.com

Look around, and you'll find the mercedes w114 ones (mine used 4 spacers; two for each carb and the corresponding gaskets as described above).

Jub

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Current:
1971 Mercedes Benz 250 (Euro Spec)
1972 Mercedes Benz 250 (US Spec)
Past:
1972 Mercedes Benz 280