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Date registered: Oct 2011
Vehicle: 1972 250/8 W1140111 / 79 450 SL
Location: Prescott, AZ. USA
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If the diaphram is ruptured it will suck fluid from the transmission into the intake manifold and smoke out the exhaust. In my case the vacuum side of my modulator was full of sludge from 40 years of driving, basically varnish from the intake seeping into the line and down to the modulator. A through cleaning of the modulator on the vacuum side of it cured my problem, but replaced it anyhow. My 72 250 W114.011 had the same problem when I purchased it, in my case with the dual zenith carbs, after adjusting the valves, checking the entire ignition circuit, replacing the points, plugs, condenser, checking the ignition wires, inspecting the cap & rotor, setting timing to spec. and running a compression test. I determined the the carbs as usual were the problem. After rebuilding these carbs for hundreds of customers, I know better than to run them on my personal car. The best possible solution is to replace them with the Weber/Redline conversion. It's about the same price as having yours (if so equipped) rebuilt by a pro. If you are not a real good carb man, these are purely not for the novice. The Redline Weber carbs perform way better than stock and tuned correctly get decent fuel mileage. There are other things that could be causing the problem, like a bad or failing torque convertor.
Hope this helps, If I still lived in Pasadena I could help...