Need help with 1969 250C Zenith carb rebuild problem - Page 2 - Mercedes-Benz Forum

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post #11 of 16 (permalink) Old 11-05-2013, 02:58 AM
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Sorry, it´s the front one only, the rear one has the vacuum box.
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post #12 of 16 (permalink) Old 11-06-2013, 08:53 PM
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Originally Posted by javimx5 View Post
Sorry, it´s the front one only, the rear one has the vacuum box.
yes its the vacuum operated idle control.
Like to know which is the best source of carb repair kits .Royce is a bit disappointing in that the gaskets are thinner than original ones and the zenith's are prone to warpage .
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post #13 of 16 (permalink) Old 11-06-2013, 11:30 PM Thread Starter
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FOllow up on Zenith Carb rebuild problems

Well, I worked on these "babies" more last night. I think I have the idle problem solved!
And ctaylor (see post above) was right. throttle plate.

I had made a stupid mistake. I tried to set the idle and sync the two carbs with the link between them connected. This will NOT WORK! Don't know what I was thinking.
Once I disconnected and went back to set the idle, it was clear the rear carb idle was set too high. The "dribbling gas" was the result of too much vacuum. When I set the idle, problem went away.

I set the idle and set the mixture on each carb (see next post), THEN adjusted the link and reinstalled. Now they work pretty good. Only problem left is a choke plate on front carb that sticks open after engine cools down (feels like something is rubbing on the rod).

Thanks again!
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post #14 of 16 (permalink) Old 11-06-2013, 11:39 PM Thread Starter
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Rich mixture adjustment

Over 75 sent a great link to a bunch of info on these carbs. One of the best was this link.
Google Translate

The site is German, but notice the link is a google translation. At the end of this article is a paragraph on how to set them mixture screw without a CO2 monitor. However, the translation leaves a lot to be desired!
Can anyone figure this out:

"There will always be first adjusted the mixture, then only the synchronization. A CO monitor is not required, if you do it exactly as I have described. When rotating the screw in a given direction increases, the idling speed. If one continues to rotate in the same direction, they eventually fall back. This transition between max. Speed ​​and then the speed traps is the optimal point. That is, since the mixture is 99% of the optimal and then CO is true. If you have the will (also called idle screws) with the Rändelschräubchen turned the speed back down to the optimum level. Always true to the speed a little on each carburetor and carburetor but ALSO both have the same vacuum."

Since I have no CO2 gauge, I could use some advice on how to set it.
Thanks again.
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post #15 of 16 (permalink) Old 11-07-2013, 02:06 AM
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Great rectification!
Regarding the rear carb dribble i would say carb sync did the job,could not be too much vacuum as it is same in the engine but increased airflow in one carb could have been the problem.
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post #16 of 16 (permalink) Old 11-07-2013, 02:45 PM
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I have always started with the idle mixture screws out two turns or so, and then turned them CCW maybe 1/4 turn at a time, keeping the two in sync, until the idle speed "plateaued."

Nice work getting the car to run right.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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