Yes, the 2.5 and 2.8 single-cam sixes built from '65 to the mid '70s did have seven main bearings. That British car-mag is the only source I've seen that mentioned a four-bearing M123 engine. Perhaps Mercedes had some left-over tooling or materials from the M180 production to justify reviving the four bearing six one last time.
I know the ealy M180 220 engines had a double-row timing chain, while the M180 230 engines went to a single-row - perhaps without the severe durability problems that afflicted the early '80s US 380 V8s, but still....

Note - On the Diesel Forum there's a posting from an unhappy 240D owner lamenting his broken timing chain. Those engines have a doble row chain!

Happy Motoring, Mark

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DrDKW

The carb clean and rebuild is no big deal. You buy a gallon can of carb cleaner at any auto parts store. Remove and disassemble the carb and put the small parts in the basket that come in the can. Put the larger pieces in the can, or maybe in a separate pan. Let everything soak overnight.

Rinse everything with a fine spray of water and blow all the water out with air - Sears sells a small compressor (no tank) that works fine. Pay particular attention to the idle passages and other holes where fuel and/or air pass. Put it back together with the new pieces. Suggest you use genuine Mercedes gaskets for the large pieces.

Most rebuild kits come with directions or at least a diagram. There are directions for cleaning the carb on the 114 CD, and I'll send them to you if you send me an email.

But I have to say that you most likely have a serious vacuum or air leak somewhere, judging from the statement that you can cover the front barrels with your hand and make it run better. When you have it apart, use a small straight-edge to check all the mating surfaces.

Are you sure that your secondaries are closed at idle?

Do you have a good base gasket?

Have you looked/sprayed around the intake-cylinder head to test for leaks?

What happens if you disconnect and plug the line to the brake booster?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

right before i removed the carb today to do a cleaning, i cranked the idle up to what i imagine was around 1800-2000 rpm and watched the behavior. fuel was trickling pretty well down the left side of the primaries, but none was coming out of the right side. if you accelerated a bit more, a lesser amount of fuel would begin coming out of the right side. wondering if this is a problem, and fuel should begin simultaneously on both the mains, or whether it is 'staged' from left to right?

also, see 2nd photo: what does this big screw do? it's not mentioned in any of the literature from the w114 version Solex's.

Attached Thumbnails

   

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-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

Hi,
Your carb is likely warped as it is located over a exhaust heated hot spot that will be seized solid by now. M123 was basically updated M180 and around here ALL the W123 250s were re-engined with the M102 2.3l K-Jet gas or OM615 2.4 diesel engines. Reason: DEAD carb.
Take it apart and clean it up but don't expect it to run well for long. Check the bakelite insulator under the carb as well, it can develop hairline cracks that will mess up idle mixture as the manifold heats up.
Of course as always 'your results my vary'
I have a 4A1 on a 1980 BMW 525 E12. It was installed new in 1992 because original unit was warped and had hairline cracks in the castings that hold the jets, causing unmetered fuel to flow into the main and secondary systems as the fuel got hot. Even overtightening the aircleaner securing nut can mess up this marvel of Solex technology.
My advise is find a single point injection system and fit that---Holley had the Pro-Jection some years back.
Have a good weekend

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Nachi11744

Wow, it really does look just like a Q-jet. They are finicky things to tune re: the giant air-valve secondaries. I could never get my old caddies to transition perfectly smoothly when they opened. I think smooth transitions took a back seat to gobs of airflow when floored on those carbs. Anyway, you shouldn't have fuel dribbling inside your carbs aside from the nice sharp squirts from your accel pumps when you push the throttle. It's probably leaking through a gasket out of the bowl or someplace.

If your engine is anything like an m180 it should be pretty decent, heck they used it continuously back till the early 50's and even in the german army's unimogs! If you get it running right it should be not too bad on gas with those small primaries and rock solid durable too. The carb/heat riser deal is your only weak spot, but no reason to shun a perfectly good engine. I have faith you'll get that carb singing again (or is it cooking..) or if ya can't perhaps you can buy a bunch of parts carbs someplace and cobble one up, or just put a qjet/carter/holley/weber on it, take yer pick.

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1967 230S automatic
Boston, MA