w114 stutters from a dead stop - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 04-24-2010, 10:05 AM Thread Starter
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w114 stutters from a dead stop

I always had to baby it from a dead stop. It used to die if I wasn't very careful but now that the carbs are sync'd properly it just stutters.

I've lived with this long enough now that I just consider it a quirk of the car but if I were to fix this where would be a good place to begin?

My first thought would be rebuilding the carbs.
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post #2 of 5 (permalink) Old 04-24-2010, 10:40 AM
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It's gotta squirt.

Take off air cleaner and with motor off move throttle and look/listen for accelerator pump is activating with a slight throttle opening.
Maybe an adjustment, if not rebuild carbs, replace diaphragm.

How were these synched?
Do they have an equal high vacuum "hiss" equally at idle?

Brian O

Last edited by bostosh; 04-24-2010 at 10:43 AM.
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post #3 of 5 (permalink) Old 04-25-2010, 01:10 PM
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Bostosh is right. I am guessing you have the dual Zeniths? The accelerator pump(s) are probably bad. The originals were leather and tend to wear out after 30+ years. The new ones are Neoprene rubber and work pretty well. They can be reasonably purchased from your local, knowledgeable foreign parts dealer. They can be replaced without removing the carbs. (just the lids have to come off), which is a good thing. If you've had them properly sync'ed and all else is good with the carbs., do not ever mess with the linkage.
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post #4 of 5 (permalink) Old 04-27-2010, 07:46 PM Thread Starter
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I've had two of these rebuild kits for ages.
PeachParts FastLane Mercedes Parts Store

I assume you're talking about the rubber piece in the bottom left.

Is the accelerator pump that needs replacing the same as the diaphragm? If it is I know the general idea of how to go about replacing that, if it isn't I'm lost.

Ah nevermind it's in this picture http://www.automotion.com/product.as..._id=4295#tab_a

Last edited by EricDr; 04-27-2010 at 08:16 PM.
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post #5 of 5 (permalink) Old 04-29-2010, 04:01 PM
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No, Eric, it looks like the part we're after is the little black rubber (almost bell or cup shaped) piece just below and to the right of the top center gasket in the drawing. Or, just above and to the left of the little outside star washer. The pump rubber goes on the plunger which fits in the accelerator pump bore. With fuel in the bore, if you push down on it while looking down the primary carb. bore, you should see a stream of fuel squirt out into the venturi area. If I did it right there should be a picture of a similar one below. It is off a different type carb. but yours is very similar. On the picture you can see where the little rubber piece goes. As I said, if yours is the original, it will be made out of leather.



The function of the accelerator pump is to momentarily provide the additional quantity of fuel needed during acceleration, until the flow delivered from the main metering system increases. This is required whenever the throttle is suddenly opened.

The pump is a piston type pump, operated through the throttle linkage. It is used in stage I only. Located inside the float chamber, it is constantly surrounded by gasoline.

When the pump lever is actuated, the pump piston forces fuel through channels and out through the calibrated injection pipe into the carburetor throat.


Examine pump plunger for damage and sticking. A faulty accelerator pump will cause:

1. Hesitation on acceleration

2. Stalling

3. Fuel consumption

Test: Pump lever should have tension‹if not, pump is binding in bore
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