Need help with Weber kit - PeachParts Mercedes-Benz Forum

Glenn · #1 07-26-2003, 11:09 PM

Hello folks, I took many of your suggestions and finally bought the Weber K245 kit to replace the Zeniths on my '67 250S with 4 speed automatic trans. I've begun the changeover but, there's several items in the Weber kit and instruction sheet which don't match my car or original carb. setup. I am hoping that some of you guys or gals out there can give me some pointers. Here's what I am running into:
1) the instructions tell you to adjust the transmission passing gear rod which connects to the throttle linkage - I have no such items on my car. I have a kickdown switch which is found under the gas pedal and kickdown linkage which connects to the transmission modulating control and solenoid. Am I missing something here or are the instructions wrong or written for another application?
2) the instructions say to connect the idle cut-off leads to the Webers idle cut-off valves. Are they talking about the idle fuel shut-off solenoids used on the '71-72 models? Again, my car does not have this feature. If the Webers idle cut-off valves serve the same function as the Zeniths shut-off solenoids, this would be a good idea to go ahead and use this system. I belive all that is required is to run a wire from an igniton hot source and connect to the Webers cut-off valves.
3) my Zeniths have the idle lifting switch found on the front of the front carb, which I believe controls the solenoid on the transmission I mentioned in item 1 above. The Webers do not have any provisions for this and I feel it is very important that I do something about this. Have any of you found a way to make this work. I was thinking about installing a N/O switch somewhere on the throttle linkage and adjust it to open at the specified 1400 to 1600 rpm. If any of you knows of a good location for this switch, please let me know - or if you have a better suggestion, I am all ears. Thanks to all of you for your past excellant suggestions and comments. Glenn
PS those nuts holding the Zeniths on the valve cover side sure are a bear to get to. I managed to get all but one off and had to modify a 12mm wrench to get the last one loose.

Mark DiSilvestro · #2 07-27-2003, 12:24 AM

!. I'm mainly familiar with the 280S and W114 250 models from 68 to 72. On those cars with automatc, there's a bellcrank bolted to the engine block under the manifolds, behind the alternator. The rod from the firewall pedal linkage connects to the bellcrank. Another rod connects the bellcrank to the carbs and a third rod passes from the bellcrank, under the manifolds, to connect to the shift modulator control lever on the transmission. If your 250S doesn't have this setup, I'd disregard that part of the instuctions

2. You're correct about the idle solenoids.
I recommend adding a fuse in the circuit from your ignition power source.

3. According to my '59-'67 Mercedes shop manual, Those early automatics (except diesels) used a double acting solenoid for trans modulator control. The solenoid is mounted on top of the tranny case and moves the modulator linkage to 3 positions. The linkage moves forward when the accelerator pedal is floored (kickdown), the linkage moves rearward when the pedal is released (idle position) and the linkage moves to center (solenoid in neutral position) at all other accelerator pedal positions between 1200 RPM and full throttle. According to the manual, the carb switch should be off/open above 1200 RPM so adjust accordingly whatever switching you fabricate for the Webers.

Happy Motoring, Mark

ctaylor738 · #3 07-27-2003, 03:33 AM

and taking the valve cover off really helps getting to the carb nuts.

You should also make sure that your heat risers are either working or jammed shut so you don't fry your new carbs. Many posts on this.

Glenn · #4 07-27-2003, 08:20 AM

Gees guys, thanks for the fast replys.....

Mark, thanks for the very valuable input.
1) I thought I should just disregard this portion of the instructions as my car does not have this linkage. I imagine that Weber writes their instructions based on the various models and applications out there, and there are obviously many!!!
2) I can connect to the under hood fuse box, which I already replaced with a 6 fuse box. All are wired to be hot only with the ignition on, so this circuit would be perfect, plus I'd have the fuse protection you suggest.
3) your explaination on the double acting solenoid really helps me to understand the importance of making sure I do go ahead and install a switch for it's operation.

Chuck,....take off the valve cover........I feel like a fool.....it would have made the job so much easier!!! I have the heat risers jammed shut and there they will stay. Thanks for the pointers.

Glenn · #5 07-28-2003, 03:09 PM

I emailed Weber with the same 3 questions I listed here on this forum and here's their response:

"You are right on #1 and #2....#3 does not have anything to do with the trans. It was a carb function only and is not needed...."

I agree with them on items 1 & 2, but from what I've learned (mostly from Mark) they are way off base on item 3. And according to the Zenith troubleshooting manual I downloaded last year, if the idle lifting switch is not operating properly, the transmission may do more than just not shift properly, it could be damaged.

Do any of you have any input on this reply from Weber?

Thanks, Glenn

Mark DiSilvestro · #6 07-28-2003, 05:01 PM

As Weber hasn't explained what 'carb function only' that switch is suposed to perform, I will have to rely on my '59-'67 Mercedes factory service manual, under 'Adjustment of Idling Switch' which states -
"If the idling switch on a [fuel injection] venturi control unit or a carburetor has been replaced it must be properly adjusted. The adjustment must be checked when there is trouble in the electrical system of the automatic transmission (e.g. racing of the engine, slipping of servo members, no braking shifts when driving down a grade at more than 1200m above sea level)."
Unfortunately, my factory service manual doesn't have a picture of this switch so I have no idea of how or where it mounts to the carb. (My 220S is a stick-shift)

I did find an automatic trans wiring diagram in the Mercedes section of my 1966 Glenns Import Repair Manual. It shows a crude drawing of a square switch, called an idling or lifting switch, with a round shaft sticking out of the center, but again no picture of it's attachment to the carb.

I can't think of any other electrical switch on the carb of a mid '60s Mercedes, although the '70s carb models proliferated with sensors, switches and relays for emmissions control. Those cars used the modulator rod connected directly to the throttle linkage and dispensed with the double-acting solenoid.

Happy Motoring, Mark

ctaylor738 · #7 07-29-2003, 02:24 AM

I think Weber is confused and that you and the good DrDKW have it right. Some of the Zeniths had a fuel return valve mounted on the front of the front carb, and THAT is a carb function and Weber may be confusing it with the trans function.

ScooterABC · #8 02-28-2012, 07:56 PM

Well I have to say, GOOGLE really is wonderful. I've been trying to find out how to resolve the issue of the lack of weber switch for the transmission modulator solenoid and I found this thread!!! Too bad it is a 9 year old thread. Oh well, I recognize a name or two so maybe someone will respond.

I'm in the same boat regarding Glenn's item 3. I have the two wires that tell the transmission that the gas pedal is not being pressed, but nothing to connect the wires to.

How was this resolved? Did you fabricate a switch? Did Redline or Weber offer a solution?

thanks
Scott