Solex 4A1, 1975 - PeachParts Mercedes-Benz Forum

Jayeff · #1 09-25-2009, 12:06 AM

For all U vintage freaks. Yeah, we're out there.

Solex 4A1 for the M110

The infamous Solex 4A1 has been the bane of MB owners. But 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 accelaration, 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 carbureter, 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 adustments 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 accelaration 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.

Jayeff

'73 280, '75 280, 86 560 SEC. '58 Jag XK-150 DHC, '54 Jag XK-120 Roadster, '98 Chevy Lumina, '79 Dodge D-100 Pickup, 92 GEO Metro.

Takernz_30 · #2 09-25-2009, 03:39 AM

Jayeff,

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.

JMURiz · #3 09-25-2009, 10:07 AM

Good, encouraging post.
The more I read up on the quadrajet, and solex 4A1, the more I realized they were good carbs when built right and adjusted.

Thanks for the tip on the home made gaskets. Question, does the home made one replace the stock one or do you put them both on?

Bill Adkins · #4 09-25-2009, 11:03 AM

That carb started here in 1973, it had several versions the lastbeing 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 heigths. We also plugged a vent hole in each throat for tip signal and re=located 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 traveled 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 mods. somewhere.
Bill

Jayeff · #5 09-25-2009, 10:20 PM

Quote:

Originally Posted by Takernz_30

Jayeff,

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.

I used an older Canon PC-25. It has a straight in paper feed. Could be a problem with new copier/printers. The idea is to copy an exact image on the gasket paper. Where there's a will, there's a way (mom used to tell me).

Jayeff

Jayeff · #6 09-25-2009, 10:33 PM

Quote:

Originally Posted by JMURiz

Good, encouraging post.
The more I read up on the quadrajet, and solex 4A1, the more I realized they were good carbs when built right and adjusted.

Thanks for the tip on the home made gaskets. Question, does the home made one replace the stock one or do you put them both on?

Use the new ones (all 3) in place of the OEM gaskets.

Jayeff · #7 09-25-2009, 10:51 PM

Quote:

Originally Posted by Bill Adkins

That carb started here in 1973, it had several versions the lastbeing 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 heigths. We also plugged a vent hole in each throat for tip signal and re=located 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 traveled 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 mods. somewhere.
Bill

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.

regards,

Jayeff

Bill Adkins · #8 09-26-2009, 02:26 AM

Actually you are correct as to the importance of sealing the top and the base. If a person had access to a chassis dyno as I did back then he could tune the secondaries specifically to run with the engine and car combo..... weight being the issue. If I remember to look I might be able to find some specs that apply to that motor.
Bill

wolf_walker · #9 09-26-2009, 08:26 PM

I had thought about this, and have used double top gaskets in true old-quadrajet fashion, but I was concerned that opening up the distance between everything in the top plate and the main body would alter things. Also the though of the precision needed in cutting out that gasket made me not try it. Interesting to hear success though. I'm still quite well reminded of why I quit messing with carbs after driving this one daily for the last year.

How's your MPG if I might ask? I'm still topped at 16 average.

ctaylor738 · #10 09-27-2009, 08:16 PM

Nice wrench! Finally, some hope for 4A1 problems.

Jayeff · #11 09-27-2009, 08:33 PM

Quote:

Originally Posted by wolf_walker

I had thought about this, and have used double top gaskets in true old-quadrajet fashion, but I was concerned that opening up the distance between everything in the top plate and the main body would alter things. Also the though of the precision needed in cutting out that gasket made me not try it. Interesting to hear success though. I'm still quite well reminded of why I quit messing with carbs after driving this one daily for the last year.

How's your MPG if I might ask? I'm still topped at 16 average.

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 ign 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 visibability and seating position to some newer cars.

Regards, Jayeff

JMURiz · #12 09-28-2009, 04:27 PM

I have the factory manual for the M110, with the Solex 4A1 setup info in it. Seems to have a lot of info, if your carb is in good working order, mine doesn't seem to be in tip-top shape though.

Has anyone on here from the DC area done a setup or rebuild on a 4A1? I'd love to get mine running on on all 4 barrels.

wolf_walker · #13 09-30-2009, 09:17 PM

That is impressive mpg. I'm just content that mine idles and starts and such anymore. I'm not new to carbs by a long shot, and I've thrown up my hands
long ago with this thing. Been a good reminder of why I like diesels so much.

Takernz_30 · #14 10-02-2009, 09:38 AM

Jayeff,

How many of your home gaskets did you put on your 4A1? the 3/32" gasket paper i mean? did you apply some sealant in between the gaskets? my 280S is showing symptoms as you said earlier, but I have to adjust the float valve b/c I saw dripping fuel to the throttle.

Sev · #15 10-07-2009, 04:31 AM

if anyone wants a practise solex, i have a couple laying around, pm me