My Mother-In-Law got nostalgic early this year and purchased a 1976 280S twin cam 4BBL six. The car has 78000 miles on it and is in decent cosmetic condition for its age. Unfortunately, she has not been able to find a competent mechanic in her area that can get this car to run and idle right.
Up to this point, it's had: Ignition tuneup,by a 'trusted' garage on Ventura Blvd who charged her 50 bucks for a 7.00 gas filter, $419.00 for $215.00 (retail) worth of parts, a carburetor rebuild by a MB shop (who told her after a $750.00 rebuild that "this type of car still needs to be warmed up at least 5 minutes before getting underway").
It still dies in traffic, idles like it's got a vacuum leak, and gets 12 mpg (carb set rich to compensate for vacuum leak?).

I'm going down there in 2 weeks with my tools and MityVac tester and am prepared to tow it up to the Central Coast area if I can't troubleshoot it there- at least I'll get it away from the gaggle of grease monkeys that can't fix this thing.
It still has a leaky exhaust manifold and a shot diverter valve in the smog pump system that makes a horrible noise, but NOBODY seems to have noticed this. Instead, another hack has tried to sell her on replacing the intake manifold to make it run quieter!

My questions to all who have been so helpful with my 300D--
1) This engine is not rocket science, but is there anything tricky I should watch for in diagnosing this inability to idle?
2) it has the California A.I.R. pump- I believe this car does not need smogging due to its age- would it hurt the carb settings if I just yanked all that stuff out?
3) what type of fuel economy should I expect from this twin cam (city & highway)

Thanks in advance for your thoughts and assistance! (she should have got a diesel IMHO- I love mine much more than she loves hers!)

Nate Stanley
'79 300D
'85 F-250 6.9 diesel

There were more mods & service bulletins on this CARB than any other subject durning the 70's. Most techs today have no idea how to fix them, & neither did Mercedes!! Find another way to waste $$$$$$. Warpage of the top of the carb caused many problems. At one time a company called JAM ?? offered a bolt on Holley/Webber carb. It uses a "spread-bore" bolt pattern.

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 16V ITS SCCA racecar

Geee, that wouldn't be the Solex 4A1 carb, would it? That blasted piece of #$%# has caused me more grey hairs... I've cussed at it, fiddled with it, messed with it, tinkered with it, adjusted it nine ways to sunday...you think the damned thing would stay running?? Hell no.
I can't even find a mid seventies 4bbl GM carb that I might be able to jury rig to the blasted thing. Oh sure I could send it across the state and have it rebuilt for $500, and I'm sure it would look pretty, and may even work, but it's not like I have $500 to throw around on something like that. (BTW, when it does run, the DOHC 6 sounds sweet!)
--Thanks for listening...grant me this vent, its my birthday. :D

OK, guys-- it's 2 strikes in the first inning, not quite ready to forfeit the game- Let's bend the rules.
Is there anyone out there who has done some sort of conversion to a workable carb?

Keeping options open,
Nate

Once the top is warped there isn't any way to repair!! Some times these things just aren't repairable. Remember the $750 & still doesn't run right?

Well, here I am. Went to work for a MB dealer in 1974. Spent three years there and a life time later. I can fix those carbs. Don't expect to find many others able to say that. Don't expect to find many who care.

I don't know where to start about repair. You almost have to be there. MBDoc has the final blow spelled out. Once the top is warped, heroics are necessary. Aside for a bushel of mods and adjustments, timing is ever so important with those motors. Most carb problems can be partially masked by a few degrees of timing.

If you want to fix the carb let me know.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Many thanks to all who responded to my 280 questions!

I went down there over the weekend to find that the car was running better since the carb rebuild, but was still gulping fuel and running way under its potential.

Manifold vacuum was 10-12" HG, timing appeared close to the 4 deg ATDC with advance as stated on the emissions placard .

Acting on a hunch that the distributor was installed 1 tooth off (please correct me if I could be wrong)and ignoring timing marks, I advanced the timing enough to bring manifold vacuuum up to about 18", and took her for a spin- Lots more power, no overheat or pinging! I also had to back off the idle speed about 1000 rpm after advancing the timing.

Bottom line was that after all the $ spent on this car, it was running severely retarded and almost drowning in its own fuel!

the only problem now is excessive richness at part throttle during acceleration- I get a stumble and a poof of black smoke until the engine gets on the cam.

3 questions remain for discussion.

1) Since I didn't have a manual, I didn't attempt to try to reinstall the distributor. Is it possible to get these in one tooth off on the drive gear? If that's not the case, do these engines have a harmonic balancer that could slip and cause an erroeneous timing reading?

2) Intake manifold appears OK. What needs replacing is the leaky front exhaust manifold. Does this unit have a cat converter built into the manifold? Any ideas about approximate cost?

3) Not wanting to get anyone in trouble, but- would it help to remove the A.I.R. system (smog pump)and related plumbing on this engine?

thanks for your help,
Nate Stanley

'79 300D
'85 F-250 6.9 diesel

Nate:

I have a 71 250C - SOHC M130 engine which is different than the one in the 280C. However, some things seem the same. I replaced my Zenith carbs with Webbers and upgraded the ignition system and still had some of the problems you describe. My timing spec was also 4 after. I set it to 12 degrees BEFORE and now the car runs as I would expect it to. My research indicates that the late (retarded) timing was MB's early attempt at emissions control, along with some other 2 and 3 way valves, etc. Anyhow, I doubt you distributor is off a tooth - I think you have what I had - just a factor retarted timing setting.

Another issue. Yes, JAM Engineering (Monterey, CA) has a Holly conversion for your engine. I have talked with John at JAM a few years ago - nice person. At one time he gave a 25% discount to MBCA Members. Check out their web page at www.jameng.com - lots of neat stuff along with prices, etc.

Hope this helps.

Dan



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Dan Taylor/ Tulsa, OK MBCA '71 250C/'81 300TD-T

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Nate Stanley:
My Mother-In-Law got nostalgic early this year and purchased a 1976 280S twin cam 4BBL six. The car has 78000 miles on it and is in decent cosmetic condition for its age. Unfortunately, she has not been able to find a competent mechanic in her area that can get this car to run and idle right.
Up to this point, it's had: Ignition tuneup,by a 'trusted' garage on Ventura Blvd who charged her 50 bucks for a 7.00 gas filter, $419.00 for $215.00 (retail) worth of parts, a carburetor rebuild by a MB shop (who told her after a $750.00 rebuild that "this type of car still needs to be warmed up at least 5 minutes before getting underway").
It still dies in traffic, idles like it's got a vacuum leak, and gets 12 mpg (carb set rich to compensate for vacuum leak?).

I'm going down there in 2 weeks with my tools and MityVac tester and am prepared to tow it up to the Central Coast area if I can't troubleshoot it there- at least I'll get it away from the gaggle of grease monkeys that can't fix this thing.
It still has a leaky exhaust manifold and a shot diverter valve in the smog pump system that makes a horrible noise, but NOBODY seems to have noticed this. Instead, another hack has tried to sell her on replacing the intake manifold to make it run quieter!

My questions to all who have been so helpful with my 300D--
1) This engine is not rocket science, but is there anything tricky I should watch for in diagnosing this inability to idle?
2) it has the California A.I.R. pump- I believe this car does not need smogging due to its age- would it hurt the carb settings if I just yanked all that stuff out?
3) what type of fuel economy should I expect from this twin cam (city & highway)

Thanks in advance for your thoughts and assistance! (she should have got a diesel IMHO- I love mine much more than she loves hers!)

Nate Stanley
'79 300D
'85 F-250 6.9 diesel<HR></BLOCKQUOTE>

Had a 1974 280C, same basic engine/carb setup but without cats. Mine was running excellent and still only got about 14MPG on the highway. The US version of these engines are really bad on gas mileage and only have 120hp versus 157hp on the euro which gets about 20MPG on the highway. Regarding the smog equipment, 1976 vehicles are still required to pass smog, only 1973 and older are exempt. Unless you can get a knowlegeable tech to work on the Solex, you are better off converting to Weber or Holley.
I believe for 1976 the cat is down the exhaust pipe not on the manifold. Hope this helps.
Regards,
Joe Brasileiro

The US catalyst on all carburated M110 motors were on the manifold visable from the top.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician