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My Solex to Weber Conversion: Pictures and Notes

Started by agav, 01 March 2016, 10:57 AM

s class

I'm bumping this up because I'm battling with a 280S at the moment that has a butchered vac system.  The car is on the original solex, and I'd also like to know where each of the ports on the solex was originally supposed to connect. 

Forgive me, I know D- and K-jet very well, but carbs are still a black mystery to me.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

agav

I will draw out what I see under the hood today, and add a diagram I found. Maybe we can figure it out together!
1975 W116 280S in Topaz Brown - my project

UTn_boy

S Class, what year is the 280S that yo're working on?  Different years had different vacuum routing.  Also, the factory M-110 engine service manual has the routes laid out. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo

agav

#18
Before I get back from work and can dig into what is going on under my hood, thought I'd share what I found so far. Unfortunately the links on the service manual section of this site all work EXCEPT for the vacuum diagrams. What are the odds!

This might be a useful link though:
http://peterschmidtransmission.com/mb_files/vacuum_schematics_68-79.asp

That's where I found this which seems to fit my model:
1975 W116 280S in Topaz Brown - my project

agav

I mapped out the vacuum connections on my car today. For the most part, they actually fit the diagram I posted above.

I circled the connections that would have gone into the Solex and are currently not connected in red.

I'd love any help in figuring out if I need to hook up vacuum advance and retard from the Weber (it has both) to any of these lines – to be honest, I am not sure which of these are critical functional components controlled by vacuum: EGR valve, air pump, purge valve (did I miss something?).

There is also a vacuum port on the intake manifold, but it seems connected to entirely different functional components.
1975 W116 280S in Topaz Brown - my project

s class

Quote from: UTn_boy on 11 March 2016, 12:56 PM
S Class, what year is the 280S that yo're working on?  Different years had different vacuum routing.  Also, the factory M-110 engine service manual has the routes laid out.

Hi,

Its a 1980 euro spec.  No emission controls whatsoever.  It does have aircon, so the distributor is plumbed for vac advance and vac retard. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

ronw123w124

So whatever happened to this conversion? Just purchased a Weber carb kit to replace the Pierburg that's currently on my car. I hope to see some updates on this.

agav

Hi there! Great to see we still have interest in this!

I have been traveling a ton and was planning on working on this today... Last piece is the vacuum setup as stated above. I am not sure where to fit this to the Weber as I only have two ports - vacuum advance and retard. See my sketches above. Maybe someone has some thoughts on this.
1975 W116 280S in Topaz Brown - my project

foreste2002

Hi...this is really great info!  I am in AZ and have a 1968 250s with a bad motor (long story).  I came across a low mileage M110 motor with fuel injection and transmission.  I plan to put this motor and trans into the 250s...it should fit nicely.  I also came up with a cylinder head off a 1975 280s with the solex 4a1. and intake.  So, I want to get the m1110 engine running to see what I have...do you think I can get the solex with the intake put on the Injected block running fairly easily without all of the vac. hooked up since I won't have any pollution equipment?  I would love to get the injection setup going but it has been sitting for quite awhile and maybe after the motor runs....adding a Megasquirt system or similar. 

Any thoughts or ideas?

Eric

agav

I can't answer your question directly, because I don't know enough about these heads and if you can simply bypass the injection system by running a carbureted version. I would assume that there is an engine control module that might not play ball? Someone else here will know better Also, Kent from Mercedessource has a couple of great videos on how to clean out injectors.

What I can help with now is the vacuum setup though. I posted on another forum and got some advice on that, at least in my case here is what I'll do:

  • Leave all the emissions control related vacuum disconnected (essentially everything that was plugged into the carb). For good measure, I'll cap all lines so moisture stays out, but functionally it shouldn't matter since vacuum is only created at the carb side.
  • Cap off the EGR valve as well as the air pump but leave both in place. EGR valve should simply be closed all the time then which is fine.

So, foreste2002, as far as vacuum goes, in your case I am pretty sure you might only have to hook up the distributor to the carb assuming your model is vacuum advanced.

UTn_boy, maybe you can help with the last question. We talked about the little "upside down hat" for blow by. I have no idea where to escape this to, now that the old carb doesn't have a way for me to feed it back into the intake air?
1975 W116 280S in Topaz Brown - my project

foreste2002

Thank you...I also have a high mileage carbureted head that I can use if necessary...The injected head only had about 40,000 miles and the carbureted about 200,000 (wow)...although the head still looks good and I was going to send it out to the machine shop before install on the injected block which is very nice.  I really want to end up with a megasquirt system but first I need to see the car run and shift before adding more problems.  I think there is a gentleman on the 114/115 forum that I should pose the "which head to use" scenario....I will keep you posted!

Eric

agav

That sounds like a good approach... Maybe someone here can chime in if it would work :)

I plugged and tested all vacuum line today and noticed a vacuum leak in the line to the EGR valve that must have been there forever... I guess that answers the question if I need it... ;)

More tomorrow - I am trying to find out how to wire the charcoal canister etc. and the crank case blow by - more pics to follow.
1975 W116 280S in Topaz Brown - my project

agav

Ok, last challenge, maybe somebody can help me here. See the pics, issues numbered.


  • The little "upside down hat" rubber piece - previously blow by gases from it were escaped (and assuming sucked into) the back of the Solex carb. Where should I escape that now?
  • Just to verify - I am connecting the float bowl vent hose to the charcoal canister as instructed, although the Weber manual says optional.
  • It was mentioned before that in theory, I could just escape the fumes from the charcoal canister to the ground. But wouldn't they have to be drawn out by some sort of vacuum? Anyhow - how would you suggest connecting / escaping them in this setup?

Thank you all! Almost there :)
1975 W116 280S in Topaz Brown - my project

ptashek

Could you vent those to the air filter housing somehow?
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

agav

Quote from: ptashek on 11 May 2016, 09:58 AM
Could you vent those to the air filter housing somehow?

That's exactly what I ended up doing.

I think I finally figured it all out – here is the final part of my documentation, hope that helps. Anyone, feel free to ask me questions!


  • It turned out my car was indeed a California car. What I didn't fully understand was the vacuum system (see diagram above) hooked up to the Solex and they differ slightly in complexity by model which made it hard to find exact information. I figured it out now, though – there are a couple of main functional components, mainly related to exhaust recirculation, such as the the air pump and EGR valve.
  • Both EGR valve and air pump are not needed and I don't have to pass smog in Cal with my '75. So I disabled those and capped the lines off.
  • The engine case has a blow by connection (the little "hat" like grommet pointed out earlier). With the Solex, there was a hook up into intake air flow on the carb, so I drilled a hole into the air cleaner, screwed in a brass hose fitting and connected it directly. Now that should create just enough suction to siphon off the blow by.
  • I did the same for the charcoal canister / fuel vent lines - brass fitting on the air filter housing. Those are vacuum controlled, so I hooked up the control to intake manifold on the carb and made sure no leaks. I also fitted a little vacuum T-piece there with a cap so I can hook up my vacuum gauge easily for carb tuning, etc.

All assembled, she starts, she runs, she balks a little after accelerating RPM sharply and dropping back to idle which I was able to fix adjusting idle speed up slightly (think screw all the way in was just too low).

I have to overcome my anxiety actually driving her out of the garage (because I am on a hill and if it doesn't work out I am stuck with a tank at the bottom of the hill  ;D). But I think it should be working and although it took me so long because I have been really busy at work and procrastinating a bit, it was a great learning experience!

Posting pics below!
1975 W116 280S in Topaz Brown - my project