W114 Carbs\engine problem - Page 2 - Mercedes-Benz Forum

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post #11 of 93 (permalink) Old 04-23-2013, 08:12 PM
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What planet?

The Zeniths are fine carburetors, but they suffer from warping because of excess heat from the exhaust manifolds. This is caused by the flaps in the heat riser mechanism sticking in the open position, rather than closing as the engine warms up.

Once the warping, usually of the top plates, occurs it is nearly impossible to get the carbs to work right. The warping causes air leaks which cause high idle and backfiring on acceleration. The attempted fix is overtightening of the screws that hold the top plate to the carb body, which generally makes things worse.

In this situation, the only way to get the car to run right is to find a set of un-warped carbs, or go the Weber route.

I have owned five 250Cs and worked on many others. I have spent a lot of time ajdusting Zeniths and trying to fix their air leaks. I will say that the best running 250 I encountered had Webers.

Chuck Taylor
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post #12 of 93 (permalink) Old 04-23-2013, 08:51 PM
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Chuck
Very correct ,also happens with a overheated engine.
i had the carb surfaces done on a CNC machine and it took care of the warped top plates.
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post #13 of 93 (permalink) Old 04-24-2013, 06:27 AM
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Originally Posted by adler View Post
Chuck
Very correct ,also happens with a overheated engine.
i had the carb surfaces done on a CNC machine and it took care of the warped top plates.
Exactly. I did this on a W108 I had with the M130 and dual Zeniths. Worked like new and was far less expensive than replacing them with something else.

First thing you want to do on this setup is make sure the heat riser flap is working properly.

Dan
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post #14 of 93 (permalink) Old 04-24-2013, 08:57 AM
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i am looking at the pictures of cam shaft , i notice that some cams are shinny all around , this indicate of tight valves , with a cam pointed upward , you should feel some looseness at the rocker arm , if it feel solid , you need to loosen / adjust .4 th on int and 7 th on exh
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post #15 of 93 (permalink) Old 04-24-2013, 12:31 PM Thread Starter
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I take the intake is on the right and exit on the left looking from the front? I got the tool today and will check.
How do I check of the heat riser flap is working properly?
Thank you


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post #16 of 93 (permalink) Old 04-24-2013, 01:02 PM
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I'm doing this from memory, so someone please correct me if I'm wrong....

Both manifolds are on the right side (passenger) of the car. They are sort of "intertwined" with each other, but under the carb will be the intake plenum, or area where the carb base is located.

Directly under the plenum is a square area of equal size that is a part of the exhaust manifold. If you look at this closely, you'll see a shaft projecting out of it with a flat wound coil spring, sort of like the spring you see in an automatic choke housing.

On the opposite end of the shaft is a weight that moves against a pin that projects out of the casting. This is a stop for the movement of the shaft.

You should be able to turn the shaft freely, with it only turning a partial rotation in either direction.

If you split the manifolds you would see a flap that the shaft goes through. This allows exhaust gasses to heat up the plenum underneath the carb, warming the incoming air/fuel mixture before it goes into the cylinders.

If the shaft is frozen in place, the flap is either open (heating the plenum at all times) or closed (not heating the plenum at all.)

You can grab the shaft with a pair of pliers or ViceGrips and see if you can move it, but don't get your hopes up. Best thing short of separating the manifolds to get to it is to soak both sides of the manifold where the shaft projects out with some good penetrating lubricant and let it soak.

Dan
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post #17 of 93 (permalink) Old 04-24-2013, 01:46 PM
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Hi All
I would suggest that if you had a carb problem you would have a problem with either cyls 1,2 and 3 or 4,5 and 6 rather than the pattern you have, have you made certain that you have not crossed some wires although it would be either two or four cylinders that would be effected I suppose, also have you carried out a compression test?
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post #18 of 93 (permalink) Old 04-24-2013, 02:25 PM Thread Starter
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I have confirmed the cables are correctly connected with a working car

i have checked for the flaps and here are my findings:
The second from the front moves freely and the spring was out, i touched it and came out. i don't know which is open, which is closed position but moves freely.
i will need a spring for that one.
The first from the front is missing the spring too and it is solid stuck, i can't move it at all. i have sprayed some penetrating oil and will try again.
I can confidently say that these have been in this state for a long time due to the rust on both.


my questions are:
how is the plate affecting the working of the engine?
since this is not working as designed how do i fix it? is there a flap spring kit?
few pictures.

Thank you.
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Last edited by kavadarci; 04-24-2013 at 05:48 PM.
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post #19 of 93 (permalink) Old 04-24-2013, 07:00 PM Thread Starter
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I also found this picture (this is not from my car).
if you look on each side of the weights they have these stopers that stop the weights at that position. Mine are broken and don't stop there.
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post #20 of 93 (permalink) Old 04-24-2013, 07:37 PM
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When I was working on mine back in August of 2012, I too noticed on mine that the one on the left (see arrow on photo)
the spring was broken and it moved freeley. It is still broken and the one on the right is pretty tight and it doesnt move
if I try to push it by hand. With my engine running and idling, I move the one that is broken on the left and I don't hear
or notice any difference to the engine. I always wondered what that thing was and what it did. The condition that it is in now,
the car is still running really good.
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