'74 280C Solex 4A1 running rich at speed - PeachParts Mercedes-Benz Forum

#1 09-09-2002, 08:55 PM

I'm a newbie with a '74 280C with 113,000 original miles. The car is is pretty good shape but the price was right @ $1.00. The dealership that serviced this car finally could not look my mother in the eye when she brought the car in for service.

I went to drive it 220 miles home and found that it runs fine cold, idles a little rough when warm but runs incredibly rich on the highway. It smoked alot when there was a need to coast (as in downhill-definitely engine speed related) however, it did not happen all of the time. However, there was a TREMENDOUS plume of smoke on throttle tip in at speed. This was enough to create entire smoke screens that were visible for minutes after...

Is there a reasonably priced re-build kit for this (dreaded) Solex 4A1?
Is there a source of information that I can buy about the entire car? (I just drove it home with fouling plugs yesterday!)
Is there a Solex manual? The car is stock and used to run great, lots of power and very smooth. Now everything else is great except that I have become a gross polluter.

All responders- I am completely new to the world of MB's and it has been at least 15 years since my last carb rebuild, so....type slowly, use big letters and small words. I am not a dolt but could seem like it due to my complete lack of knowledge!

Thanks in advance!

Is that carb humor?

Dave

psfred · #2 09-09-2002, 10:44 PM

Dave:

Probably rebuild time. You most likely have a leaking needle valve, so gas pours down the air vent into the venturis from the top, worse as the speed picks up.

A minor rebuild kit will do you nicely -- new accelerator pump diaphram, needle valve and seat, gaskets. Don't touch anything else, just flush with carb cleaner. Unless there is varnish in the fuel bowl (unlikely these days), do the minimum.

Check the operation of the vac operated air vavles on the secondaries, too -- it is possible the servo is dead and you are sucking gas out with manifold vacuum since the air flaps don't open (like a Quadrajet).

Still think a stuck float/leaking needle valve is most likely.

Change the oil, too -- at least check to make sure it is oil and not half gasoline! I once fixed a Holley 2300 on a Dodge van with a stuck float, then when to move it, only had 5 lbs oil pressure. We drained 8 quarts out of a 6 quart pan......!

Peter

leathermang · #3 09-09-2002, 11:21 PM

The m110 engine manual has pages and pages of modifications recommended for this carb... also check the TSBs ... which also have suggestions... plug your car into these sites for the names of the tsbs which apply....

http://www.nhtsa.dot.gov/cars/problems/tsb/central2.cfm

http://alldata.com/

I think a Weber sounds good as a replacement...sometimes things came from the factory that are not worth the time and money to keep going 25 years later.... maybe this is one of those times...

ctaylor738 · #4 09-10-2002, 12:56 PM

The smoke on downhill sounds more like a vacuum pump diaphragm problem than fuel. Try bypassing the vacuum pump by connecting the booster directly to the intake manifold and see if that improves the situation.

Agree that that a float or needle valve problem is likely, but you might also check if the fuel return valve is functioning.

#5 09-10-2002, 09:36 PM

Dear PSFred,

Thank you very much for replying, I really appreciate your knowledge!

Last to first! I have already checked the oil and changed it! Even though the oil was changed 225 miles ago, I was sure that it was more than a little contaminated. I also have had very bad luck trying to use gas as an oil substitute!

Where can I get a minor rebuild kit for this carb? My thought here-least expensive and most probable solutions first, then the more complex later. (See other posts, serious belief that there is no value in this 4a1 Solex, better to R & R). Is there a website or a preferred house to acquire these parts?

However, I do not have a carb manual or even a model manual on this vehicle. I am sure that there are Chilton manuals or Bentley manuals on this model but have been unable to locate them. I think they would be a really good investment for me, since there is no bad winter project car! If you know of a source, or an alternative to the above thoughts, please advise...

I do not know how to check the the vacuum operated air valves on the secondaries (see prior paragragh). Thanks again for your help.

Sincerely,

Dave

#6 09-10-2002, 09:45 PM

Dear leathermang,

How can I get a m110 engine manual? What are (is?) TSBs? I appreciate your help but am so new that I do not even know the acronyms that get used by the more knowledgeable people.

I am searching the sites that you posted this evening! Thank you for those (they will explain what TSBs are, I am sure...)

The Weber sounds like a pretty reasonable thing after a minor tune up. My mechanic has told me that he will not work on the 4A1, as it was faulty design, warps at the top, and never worked on these cars...ever! However, I know that it did it's job for at least 20 years and was actually pretty smooth. So, in an attempt to keep it original (Okay, really save money) I need to find a source for a minor tunup kit. Any recommendations?

Thank you again for you input, I may be replacing sooner than I had hoped. Also, what kind of Weber would you recommend and what jetting?

Sincerely,

Dave

#7 09-10-2002, 09:57 PM

Dear Chuck,

Is a the vacuum pump diaghragm included in a minor tune up kit? I forgot to mention to PSFRED and leathermang that I am getting carb cleaner and will apply liberally tomorrow.

I have not had a chance to take off the airfilter housing for a closer check yet. However, that massive smoke screen that was emitted during throttle tip in was more than a little scary. I will try to bypass the vacuum pump and reply via email later this week.

Thanks for the reply and the sound advice. I have tried to read every 280 C thread in here and have seen your name and sage advice often (along with PSFRED and LEATHERMANG and a few others) and look forward to being able to offer solutions to others in the future. As of now, I lack even a solid engine manual or even Chilton's manual but will be all over that over the weekend!

Sincerely,

Dave

I can just feel the money flying out of my wallet! (Balanced thought-just spend less that the value of car)

ctaylor738 · #8 09-10-2002, 10:02 PM

You can order a 4A1 rebuild kit right here on Fastlane for about $64. The part number is C9010-11283.

This model is odd to find documentation for. The engine is in the Haynes manual for the 123, which covers the diesel and gas 280 engines, including the 4A1's. The body is in the Haynes manual on the 114's.

The MB CD for the 114 has good documentation on the carb and all the rest of the car.

Your mechanic is obviously tired and frustrated. With a little tinkering and patience, most of these carbs can be rescued. Yours does not have the symptoms of warping, so give it a chance before you pop the $750 or so for a Weber kit.

The premier source for the Weber is JAM Engineering.

My .02 as we say.

#9 09-11-2002, 01:08 AM

A few questions before you DOA the Solex for a Weber:

What color is the smoke? White/blue or black?
Does it smoke upon cold start-up?
Are you getting any back fire when going downhill?

#10 09-11-2002, 09:32 AM

There is no smoke at start up. (Okay, very little). There is no smoke when cold. The cars starts without a problem and there are no special tricks to get it started. Key in, turn to 2 (run the fuel pump) and turn over. Instant start. Then the car runs very well while warming up. Lots of power, little or no visible smoke. When it warms up to average operating temp (indicated 177 degrees), the idle begins to stumble at lights and the smoke becomes visible.

There have been no backfires as of yet. However, there has been hesitation (I think due to foulded plugs) as the trip home progressed.

The color is bluish white. I have been diligent about checking the oil and there is some burning, however, I am pretty confident that there is mostly excessive gas being pumped through the engine. The amount of smoke when coasting or at throttle tip in seems to be engine speed related.

I ordered a minor rebuild kit last night and need to get an M123 engine manual to help understand all of things that are involved.

Thank you for your help!

Dave

leathermang · #11 09-11-2002, 11:43 AM

Dear Dave,
TSB's.... technical service bulletins... this is what the factory sends out to dealers to tell them what they have been getting reports back from people about something being wrong with the car, and hopefully what the factory has found to fix the situation correctly...

I would never suggest paying anywhere near $750 for a carb... they should be available off some junked sportscar from the 1960's....

After what CTaylor said I do not even know which engine you have... I had assumed it was the same as my 74 280 ...

I got my manual off Ebay...and you might find a carb there also... but sportscar junkyards is where I would start looking....

#12 09-11-2002, 02:08 PM

Yep, blue/white smoke is a very rich mixture. But am confused why it only happens when the engine is at operating temp. Seems to me if the fault is from overflow (stuck needle or float) it would do it all the time.

Am in agreement the possible causes may be the needle or float. The needle comes with the kit, but the float must be ordered separately. Time to take that baby off and see what is what. You can just inspect the float/needle with out taking the Solex off. Unscrew the 4 nuts and take the 8 cover screws out. These are different lengths so be sure to lay them out in a pattern. Take the cover off and see what is what. When replacing the cover do not over tighten the screws as they will strip out the body threads. Also, the bolts Must be torqued down. The torque spec is 10 Nm with a new flange and 8 Nm using the old flange. I torque by even numbers: 2,4,6,....Nm until you get to the specified spec.. Takes a little more time, but is the proper way to torque.

The float is subject to pressure spillage if it has too much pressure coming in. It could be possible the fuel return/pressure valve is not working as well and is often overlooked.

jayh3 · #13 09-12-2002, 01:01 AM

I too inherited a 74 280c from my mom and have had it it storage for a few years. Same thing happened. The dealer said that there was a Weber carb conversion kit that solved most of the problems and gave 25% more horsepower. I have since located a supplier that claims to have the kit for $329. The average price being $600. My mom spent $500 to have the Solex rebuilt in Arizona. Before you jump at this, I found that the flap in the air housing was not opening when warmed up so the carb was starving for air. In Arizona someone had removed the 4" hose that warmed the air filter housing. Stupid me wanted everything factory so I put a new hose on so the car was getting hot air, but the flap when it works properly opens for fresh air and closes over the hot air vent. I am selling my car or I would opt for the conversion kit and maybe a mechanical distributor. I have a California car and am wondering how to block all of the tubes to the carb. This is long winded, but feel free to email.

#14 09-12-2002, 01:30 AM

If your Mom's Solex is warped, it is better off being made into a boat anchor. Otherwise with proper rebuilding it can be saved by a little work and will save you $500. It is not a complex carb at all to work on. But again, if it is in bad shape and the 116 is in good shape otherwise, go for a Weber or Rochester. Rochester is my pick.

Just wondering. Why do you want to block all the "tubes" to the carb? Which carb? And does your car have emissions?

jayh3 · #15 09-12-2002, 12:00 PM

The carb is in good shape, but has over 5 vacume tubes attached to it. also the fuel return unit with more tubes and the air filter has four large tubes connected to it. It is a California emissions car and if I convert to Weber I have a feeling that it wont have a place for the tubes and that I would have to change the distributer to mechanical, which is probably better anyway.