250s idle adjustment procedure? - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 12-15-2011, 03:27 PM Thread Starter
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Date registered: Sep 2011
Vehicle: 1966 250S
Location: Austin, TX
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250s idle adjustment procedure?

Can anyone tell me the correct idle adjustment procedure for a '66 250s? My manual (DVD) only includes details for 220 b and 220 Sb models. I'm guessing that I should just be following the "Model 220 Sb with Zenith Carburetor" procedure, since there doesn't appear to be any instructions specific to my car and it's the closest match. It's a fairly detailed set of instructions, though, so if anyone could confirm that this is correct before I get started, I'd really appreciate it.

Tried idle adjustment using the old tighten till it gets bad and then back it off a turn method, but now I'm getting sputters on acceleration. Could be I need to go back in and re-adjust the timing, but I spent a lot of time getting that right, so I think (hope?) that it's in the carb adjustments.

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post #2 of 5 (permalink) Old 12-15-2011, 08:32 PM
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It's basically the same procedure for all the twin carb cars. You need to ge the points and timing right, then make sure that the carbs are balanced, meaning that each is pulling the same amount of air at idle. Then you secure that adjustment with the rod that connects the throttle levers. Then you can adjust the idle mixture on each carb.

The balancing is done with an air flow meter.

But keep in mind that these carbs can have warped top plates due to heat or overtightening of the screws. That allows extra air = lean mixture = sputter on acceleration.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #3 of 5 (permalink) Old 12-15-2011, 09:32 PM Thread Starter
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Thanks ctaylor738! One carb synchronizer/air flow meter on order. In the mean time I'll confirm the dwell and timing are set right (90% sure they are) and then work on enriching the fuel mixture to stop the sputter.

Really appreciate your help. The service manual on disks is a pain to use... half the time I can't tell if I'm missing steps because the manual assumes I have a higher level of auto mechanic's knowledge than I do or if its because of the way it's been sliced up and arranged to display only certain sections for each model. As far as I can tell, it never mentions any method for balancing the carbs, which is a completely logical first step.
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post #4 of 5 (permalink) Old 12-16-2011, 10:11 AM
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While you are waiting for the carb sync airflow meter,

You can use the shop vac hose to listen for equal hissing sound of the idle air.

Be sure to disconnect the linkage between the two carbs to isolate the throttle plates while setting idle. once the idle is perfect then hook the connecting linkage (lube the balls/sockets) and adjust length to a neutral position, (note r/h and l/h threads). this may clear up the throttle response.

Also your vacuum advance and sticky centrifugal weights can have a major impact.

Brian O
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post #5 of 5 (permalink) Old 12-17-2011, 06:13 AM Thread Starter
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Thanks Bostosh. Sounds like a good plan.
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