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Solex carbs

Started by Martin 280s, 08 January 2010, 06:53 AM

Martin 280s

I was just talking to another forum member about having an information pool on the Solex carb. Those who are familiar with it know how much 'fun' it can be!

What do you think? To quote an interesting phrase "Information is for sharing not gathering dust"!


not that i know anything about them, but thats the beauty of a public forum - feel free to share info for all's benefit!
1979 116 6.9 #6436
2018 213 e63
2011 212 e63
2011 463 g55
2007 211 e500 wagen
1995 124 e320 cabriolet
1983 460 300gd
1981 123 280te


It would be very nice to have this info around.

Martin 280s

I've been looking around on the web too. I've found quite a lot of things although a lot is repeated on the various MB/BMW sites. Curiously Bentley Mulsanne Turbo owners don't have much to comment about the carb except it warps! Maybe they don't do their own servicing!

I did find an interesting link about making thicker gaskets by a man who calls himself Jayeff. Here goes the thread, copied from another forum:-

Solex 4A1 for the M110
The infamous Solex 4A1 has been the bane of MB owners. However, when properly set up and working as it designed to, it gives flawless performance with the 110 engine.

The 4A1 air horn warps in time. Once this happens vacuum leaks develop and the engine stumbles on acceleration, won't idle, hard starts when cold, and becomes impossible to drive if things get bad enough.

The usual practice is to tighten everything down as much as possible. This always distorts the castings even more. The next step is to tweak all the visible adjustments, then go into the capped adjustments and tweak those. By this time things are a hopeless mess.

A rebuild kit is not the answer. Both OEM and replacement gaskets are made of a thin, hard, incompressible material that will not seal the gap.

All kinds of fixes have been devised, like putting the air horn and bowl into an oven fastened to a flat plate, dressing the mating surfaces on a belt sander, filing them etc.

My solution, which is simple, very inexpensive, and very effective is to make new gaskets out of 3 3/2" gasket paper. The gasket between the air horn and the float body is the most complicated. All the holes and their locations have to be an exact duplicate of the original. The others are very straightforward.

To do this I took a new gasket, put it in a desktop copier, and copied its exact shape to gasket paper that I ran through the manual feed tray just like an 8 ½ x 11 sheet of copy paper. Some copiers don't make a dimensionally precise image, so I made sure the copy was accurate by measuring all locations against the original.

Then I made small hole cutters out of tubing, as required, and used a fresh exacto knife and a metal straight edge, etc. It takes about two hours to cut it out. Soft music in the background seemed to help. The first time tried it I wasn't happy with the result so I made a much better one the following day. I use a softer gasket paper about four times thicker than the original (not cork).

When you assemble the carburettor, wrist tight is enough. Getting all the adjustments right can be time consuming, especially when someone has changed all the capped adjustments, which were never meant to be adjusted.

I made a chart of my beginning adjustments with parallel columns showing the changes I made as I test drove the car. It was trial and error, as I had no idea which way to go.

Pretty soon I got a feel for it and things kept improving. Once I got the car running fairly well it was a matter of a tweak here and a tweak there. It took about two months to really fine tune it.

I have no problems with stumbling in hot weather, cold start is immediate, there is no lag in acceleration with your foot to the floor, and idle is dead steady with no burbles. I haven't had to make one change in many years. Now and then I will check to make sure the assembly screws haven't loosened up, but I never have to tighten them more than a fraction of a turn.

Everything else has to be right – the spritzer diaphragm, the dashpots, the float level, the float chamber vent diaphragm (important), the TN choke, if it has one. The instructions tell you how. All the smog control plumbing has to be vacuum tight. Mercedes is usually pretty good on that. Go by the book. None of this is hard to do, it just takes patience.

So don't give up on the Solex 4A1.

I have a 1978 280S, same engine as you have there, but 3/32" gasket paper won't be jammed up in the printer? It' the same trick as making printed circuit boards in a blank PCB but I used tracing paper for that, the procedure is the same as silk printing a t-shirt.

That carb started here in 1973, it had several versions the last being the one you are discussing. The biggest thing I found was the secondary flap tension was usually incorrect. I still have the factory weights needed to set the specific model secondary springs. There was a mod we did in installing a nylon sleeve on the secondary spring bar to allow it to travel more easily and of course we set the metering rod heights. We also plugged a vent hole in each throat for tip signal and relocated them with jet drills. As you indicated, the warpage in the carb top was a product of over tightening the corner nuts. The secondary butterfly shaft would bind so I made a bar to bend it until it travelled freely. I was a foreman at a dealer when that carb was put into service and they all fell into my lap to resolve. I might still have the notes I made about the modifications somewhere.

You've got more experience. I'm not a pro. The secondaries have to be set up right. I made a weight according to the manual. So many grams, don't recall the amount. The point is, once you get the leaks stopped the carb still has to be set up right according to the big book.


A thicker gasket between air horn and float body does change the height a little bit, but it doesn't seem to matter.

Mileage-wise on the road I get 22, 23, around town 16 - 17. Depends on toe twitch, I think.

Once the leaks are stopped, the carb has to be set up right and ignition timing, plugs, wires and all that need to be looked at. I would think Any 110 motor should give about the same as mine, maybe even a little better. I wouldn't be surprised at 25 mpg from a fresh engine well set up.

MB used to have a very good factory manual on the 280, including a detailed 4A1 section with great line drawings. This was a big help.

Even today after all these years my '75 280 is a great freeway cruiser. I prefer the visibility and seating position to some newer cars.

Regards, Jayeff


Martin 280s

Quote from: gerardoparedes on 13 January 2010, 08:12 PM

This link is very good, I was going to turn it into a Word document but the link is great too! :)


This one is not for the solex, is for the Zenith, but also very good


Great idea Martin.  Came across a few links during my rebuild and found those e21 forums the most helpful but never came across the thicker gasket idea.  Very interesting.

Only have a couple of inks to add:  manual in German   similar in English.

There's some Bentley turbo stuff I have at home I'll add to the gallery too when I get home.

EDIT: 2nd link was dead, I'll have to see if I saved a copy.

Also, check for info

And don't forget the Org's library - section 07.2

This haynes manual below was helpful too

1973 350SE, my first & fave

Martin 280s

I've never seen that particular Haynes manual for sale! Do you have one?


That's a picture of mine I uploaded a while back.  Can't remember which other model/s have an m110 solex setup but there's about 6 pages on the solex, mainly to do with tuning, setting choke, idle screws.  No teardown rebuild as such. There's more info in the library in general for the solex but the Haynes spells things out in plain English rather than the sometimes abbreviated tech speak of an official manual.  In general there's just good info on the m110.
1973 350SE, my first & fave


Had a look at the Bentley turbo manual and it's over 7mb, a 90 odd page pdf file and not real helpful as far as we're concerned.  Still amazing they whacked a Solex 4A1 into an air chest to power a 6.75L barge.  Never worked out if there was any difference between the Bentley turbo Solex and ours.  Too much writing to read. ;)

However, here's that English BMW Solex manual from that broken link in my first post. 14 pages in jpegs.  You can get full res pics after clicking on each image then press the zoom button underneath the middle of each pic.  Use the scroll button on your mouse to further zoom or right click and "save as" then zoom in later from your own photo viewer.
1973 350SE, my first & fave


Quote from: gerardoparedes on 13 January 2010, 08:11 PMGerman Manual for the Solex 4A1
Thanks in advance , How can download the complete this guide ?