1975 280, will not idel, will not stay running. - Mercedes-Benz Forum

 
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post #1 of 8 (permalink) Old 10-15-2009, 04:54 PM Thread Starter
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1975 280, will not idel, will not stay running.

At first, it would idle, but when give it gas , want to die, checked acc. pump , blowed out holes, not work, took top part of carb off and cleaned it, well now, wont i idel or stay running. intake back fire, also, it will start if give it gas, and as long as i give it gas it will stay running but bogs down back fires in carb. ??,'
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post #2 of 8 (permalink) Old 02-20-2010, 06:33 PM
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Welcome to the Zenith carb syndrome. If your carburetor is the dual-barrel Zenith, good luck to you. These WARP from corrosion in the die-cast zinc metal and even if you replace it with a new one, chances are that it will be warped in its box. Just enough to screw the whole idling of the car, and the only remedy is another brand of carb if you can adapt it, then tune it to your engine.

I had two mint 280C, a sedan and a coupe and had to sell them after I tried everything to make them work.
If you get one of those cars, make sure that they are the mechanical injected kind.
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post #3 of 8 (permalink) Old 02-20-2010, 07:25 PM
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OK, a 75 had its own issues. The float valve seat would come loose and raise closing the fuel supply too soon lowering the fuel level in the carb... wont run that way. The thermal choke additional air valve would change its base setting eliminating the fast idle function cold. The idle fuel solenoids could loose power and there will be no idle. The secondary throttle plates would stick causing a non functional idle system. Did it idle before you fixed it? What exactly did you do to it and what change occured as a result . the carb is a piece but it can be made to work if no one butchers it.
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post #4 of 8 (permalink) Old 02-21-2010, 03:52 AM
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Bill, what are the other issues of the "75 280? It would be good to know what to expect as I am a new '75 280 owner
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post #5 of 8 (permalink) Old 02-21-2010, 09:24 AM
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There were a list of mods we did to attempt to resolve running issues caused by trying to comply with emissions rules. The 75 was the last year of carb usage and it wasn't pretty. the biggest thing was the carbs top cover would warp due to over tightening the 4 nuts. That would cause binding in the rear control butterfly as the bore was crooked and the shaft was straight. I used to bend a slight arc into the shaft just to where it moved freely and adjust the metoring rods, the engine was a bit lean at tip in of the secondaries so I raised the rod height to allow more fuel at initiation. I also relocated bleed ports upward in the primary throttle bores and of course the accelerator pump was in need of help so I did some stuff there. With the engine hot you need to check the choke thermostat is also hot and remove it from he carb, check the slide air valve and see its has full closure hot, it is the fast idle bleed circuit so it needs to be opened cold and closed warm. I have a book somewhere in the garage as I never threw that stuff out.
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post #6 of 8 (permalink) Old 02-21-2010, 02:42 PM
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thanks for the info, Bill! A friend and I were discussing the carb earlier last night... was wondering what to do next. I looked in some other forms and it seems that there are a few replacement carbs but they are not street legal here in california. I found this link this morning, it is old but maybe it offers some help to someone: 1975 280 6-cylinder W114 Solex 4A1 Carb problem - PeachParts Mercedes ShopForum
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post #7 of 8 (permalink) Old 02-21-2010, 07:16 PM
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Actually if you researched that forum you would find many items I posted there as well. There are a number of aftermarket carbs available for sure so the main issue is obviously smog laws. If it were me I would install an aftermarket throttle body electronic fuel injection system. Good mileage, better performance and less emissions due to better fuel metering. The manifold is after all set up for a spread bore 4 barrel. Just my thoughts
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post #8 of 8 (permalink) Old 02-22-2010, 03:47 AM
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Thanks, Bill! I will research the fuel injection system and also dig a little deeper in that forum too!
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