I had to "flex" the arm slightly to get them out of the Zeniths on my 68 W110.

On my car the choke idle adjust screw is removed from the rear carb so fast idle is controlled for both carbs by the front choke.

The diaphragm pops open the choke slightly after starting, once the diaphragm sees vacuum, to allow the car to idle. I found that this was not operating correctly on mine after a carb rebuild. The flat spot on the diaphragm rod was in the wrong place by a large amount, not enough adjustment on cover, the diaphragm was working but never contacting the arm to crack open the choke flap, thus the car would not idle till the choke cracked on warm-up. Maybe the kits were for a different year Zenith INAT or the carb kit manufacturer just made them wrong? I was able to swap out the rods from my old diaphragms, bit of a fiddle, and they worked perfectly.

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Owner of Mobil-Werks
Classic Sports and Specialty Automobile Service
1968 230 W110 +3.5 M116 & 4-Speed Manual
1985 300TDT S123
1985 500SEC C126
2022 Sprinter 3500