Infamous Solex 4A1 - Mercedes-Benz Forum

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post #1 of 7 (permalink) Old 03-26-2008, 05:41 AM Thread Starter
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Infamous Solex 4A1

Hello fellows,

I got around to cleaning this infamous carb on my 280S since I just did a 700 km trip with rather poor milleage. The carb was dirty, the choke partially stuck and secondary valves sticky.

Nevertheless, the carb base is straight and it looks generally OK.
Now before I go any further, please do not tell me about Holleys. There are none to be found here (and they dont even look that great on paper) besides, I am keeping to stock carburation as french law requires .

But my questions are pretty radical. Here goes...

First, can I disable the TN starter (i.e. set its internal piston to provide NO fuel during warmup) as this device is a waste of (expensive) fuel ?

I have the silly time delay thingy that connects to the vacuum device that pulls the rod that unlocks the secondary (gasp); can I get rid of the thingy, letting the electric choke do its job for a short while ? In fact, can I live WITHOUT a choke altogether ? I live in the north of France where it never really gets close to freezing temperature.

I want to tune this carburator for best fuel economy. We have great highways for high speed cruising (at 135-150 kph) and I virtually never use this car in the city so letting it gently come up to operating temperature before hitting the gas pedal is the way I drive it.

Any suggestions ?



Lion sur Mer
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post #2 of 7 (permalink) Old 03-26-2008, 05:50 AM
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I'm not sure there are many W126 members with experience in tuning the carburator on the 280S model. After all, MB ran that engine for only a couple of years ('79 - '81, if I remember correctly) and they never brought it to the US.

You may get better responses if you post in the W116 or W123 forums, those cars had the same engine and the carburator set-up is more common among those cars.


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post #3 of 7 (permalink) Old 03-26-2008, 10:37 AM
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Carb modifications

That solex was fitted to some of the late 116 cars here in the US and overhaul parts and procedure should be avaliable.
The question arises as to what you actually expect to do by modifying the carb to disable the warm up circuit.
You really won't be able to achieve any greater fuel economy that way as you will find yourself pumping the carn and using the accelerator pump to squirt fuel into the engine just to keep the engine running when it is cold, transitioning through the warmup phase.
The three "tricks" here to using less fuel are really not going to be very effective as a carbureted engine generally gets its best fuel economy when running most efficiently.
Those three tricks are:

-adjusting the accelerator pump to inject less fuel (this will cause engine stumble during acceleration and you will have to hit the throttle harder to make the car perform the same)

-leaning your jets (mains and secondaries) 2 or 3 numbers
(this is actually counterproductive) many applications in the US were delivered with overly lean carbs to allow the products to pass emissions testing during the 1970's and early 1980's and the results were poor power. When these carbs were replaced with aftermarket carburetion, or the installed carburetors were re-jetted and modified to allow the idle mixture to be adjusted, the drivability and fuel economy would actually increase. With the correct jetting, with the engine performing properly, you do not tend to depress the accelerator pedal as much and the car uses less fuel

-retarding or disabling the enrichment circuit
(this is actually the weakness of the Holley carbs-they have their enrichment circuit controlled by a diaphragm-this diaphragm tends to rupture from an induction system backfire and the carb will run excessively rich and can run suprisingly well for a long time)
enrichment circuits can be balanced by a diaphragm/spring assembly (Holley)
a piston/spring assembly acting on a tapered metering rod (Carter and Rochester) or an emulsion well/emulsion tube assembly with metered orfices (and different volume of metal in the tube (Weber)
I don't have a blow up of the 4 barrel solex in front of me so I can't tell which it is)
the idea here is that as the engine vacuum drops during a high load/low vacuum situation such as acceleration, the enrichment circuit will cause more fuel to go into the engine
modifications adjust either how much fuel gets added, or at what vacuum level does the enrichment circuit kick in
of course, provided that the car is running a street setup and that the enrichment circuit is not stuck in the rich position, driving habits (not flooring the car and keeping a light touch on the throttle) will make a lot more difference here than any carb mods you may make

considering that your car was setup originally for optimum power and economy and nor for emissions as were cars sold here, I'd set it up stock and leave well enough alone (a full tune up will help a lot also)
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post #4 of 7 (permalink) Old 03-27-2008, 01:53 AM Thread Starter
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Infamous Solex 4A1

Hi goofyguy and all

The reason I am looking to deleting the TN starter is that it seems to be a seventies solution that makes no sense in 2008.

This device seems to enrich (waste gas) the mixture well beyond an engine temperature where it should shut off. I note that the TN starter was originally used in Sweden only as per 1976 - carbs back then were lean jetted and devices like the TN starter used to enrich the misture when cold - in Sweden, this can be critical.

Maybe I should experiment with its internal gap (reduce it) so that it ceases enrichment around 50C (not 70C). In France, 98 octane unleaded has reached 1,47€ per liter (about 2.25USD a quart !) so every bit counts.
As a result a W126 280SE sells for more than a 380SE (200hp) !


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post #5 of 7 (permalink) Old 09-21-2008, 11:52 AM
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solex 4A1

hey there guys,
was wandering around cyberspace and came across this thread for the solex 4a1 carby.
well for starters i have a ol bmw e21 that runs on this carby and i am in the middle of overhauling it myself. have taken it apart and cleaned out most of all the gum stuck in it. found a small leaf in it even....
am going to be putting it back together again over the weekend and i was wondering if you guys could help a newbie like me on a few issues?

1) there are two manufacturers for this 4A1, one from solex and another from pieburg. and i noticed some parts cant be interchanged between these two. how about the jets? would it be ok to interchange the jets? i am rebuilding the peiburg with the solex as the parts carb.

2) about this TN starter, what is it all about and any progress on deleting it?

3) any advice that cen be given about this carb? have came across threads on how to tune it for the MB engines, would the same tips apply to my six potter as well? any build articles of it online? havent been able to come across many..

again thanks guys, hope i dont get shot down coz i got a beemer and this is a MB forum.. am planning on finding me a W123 to restore after this e21 anyways.
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post #6 of 7 (permalink) Old 09-21-2008, 01:30 PM
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Welcome to the forum!

As posted above, you may find your question better answered in the W116 or 123 pages as the 126 had relatively few carb models outside Europe.



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post #7 of 7 (permalink) Old 11-12-2008, 11:56 AM
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Copied from another thread..

What I did with my Solex was eliminate the TN choke, remove the unnecessary hoses then route the choke body hose directly from the cylinder and head file down the pin which locks the second stage before the electric choke is fully open. I also blocked off the (From front to back) right side vacuum line. Since then my car has given me a reliable tick-over and good starting. As the fuel in Brazil is poor I also upgraded the main jets to 105 from 97.5 and surprising I better fuel economy.

I hope this may help you.
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