>>>My Weber 38DGAS Installation Nightmare just Started.......Need Help.....Again

Started by ESO, 30 January 2007, 11:29 PM


Dear Members,

Here is my story, I really have no choice as I have already spent lots of my time seeking for further information. Now I would like to seek for a bit of judgment and possibly some help from here.

About 3 months ago I purchased a W116 (280S) and soon after that I realized the Carburetor has a bit of leaking and mechanical problems, and instead of buying a repair kit, I have been suggested by a few owners and mechanics to replace the whole original SOLEX 4A Carb with a Weber 38DGAS (Purchased from Top-End Performance ( http://www.topendperformance.com )) which appears to be more reliable.

One month ago, I finally managed to purchase a set of brand new Weber 38DGAS replacement kit, with some mechanics help and a day work, we managed to have the unit installed. Followed by adjusting the idle and mixture, for some reason the engine idle still rough no matter how we adjust the mixture screw. You know how frustrated it is when you really want to get the car in good running condition but in fact it has been sitting at the workshop going nowhere.

So, I started asking for help from the supplier. At 1st, Steve from Top-End Performance still sends me rather brief replies, which although did not really answer my questions. Maybe, I was too anxious to seek for help and he finds me too much of a trouble customer, therefore I have heard NO reply for the last 10 messages I have sent. Put it this way, all I need is to solve the idle and accelerating problem. I have new leads and plugs installed but when the car accelerates, it feels like (when engine is COLD) it is running 1-2 cylinders less (rough). Of course, the engine itself is in reasonably good condition, compression checked okay, etc. When it accelerates, the engine feels like there is not enough fuel deliver but after 3,000rpm, it seems to be fine. I am quite sure that there is either some setting problem with the Weber Carburetor that I have just installed.

1.Will there be any chance the Weber itself has a mechanical problem when it was shipped to me?
2. Will there be a chance that I have missed out something during the installation?
3. Is there any chance that this unit doesn't suit the car? As it seems to be a lot smaller than the original SOLEX.
4. Problem with the Carburetor JET?

Can anyone help me out?

Thank you


john skene

From what little I have picked up on Webers, you need to match the CFM flow of the carby to the original within sane limits (up to 20% more, but with a Merc - which has efficient inlet manifolds and heads to start with you can probably match the flow closely)

The lean early running sounds as though the mix is outside the recommended needle adjustment limits and the jet size may need to be changed to have it run properly, see this web site which gives fairly good instructionshttp://www.redlineweber.com/html/Tech/38_dgas_tunning.htm .


Thx for you advise. Is there any chance you think I might have received a set of Weber with wrong size JET? I have mentioned before my purchase that it was for a 280S Mercedes with M110 engine.

john skene

I just went into the Weber site and had a look at the 38DGAS, it is recommended for engines of 1300 to 2300cc. capacity, however it specifically mentions  Mercedes 280, 280C, 280S for 72-76  to use kit #K248 which includes a correctly jetted 38 DGAS carby Part #18930 020

As you have a high performance 2800 I certainly think that the original jets are the wrong size if a standard 38 DGAS carby was supplied. It may pay to check with Weber on their recommended carby jet sizes if you did not buy the standard kit.

A similar sized 6 cylinder Ford engine uses the following:
Main Jets: .160
Air Corrector Jets: .150
Idle Jets: .065
Initial idle speed screw adjustment: One half turn in
Initial mixture adjustment: One turn out
Fuel pressure: 3 - 4 psi.   



Thx again for your reply. In this case, how come the guy who sold me the Carb said it is a Kit for Mercedes W116 (280S)? will they have changed the jet already before they ship the unit out to me? Or they have accirdentally forgotten to change the jet and just sent me one with original size jet.

Thank you



I'll let John answer about the jets but I've got some further thoughts.

I just finished reading some of the Weber stuff and I couldn't find where it rated this webber for a 280. 

I don't know whether to blame the carb or not although I have to agree with John about the CFM.  I saw that the 38DGAS is recommended for Mercedes but looking at the parts diagram it looks like a two barrel not a four barrel and I can't find its CFM rating.  The webber might have bigger barrels but it might not and the engine could be starving for air.

BUT!! I've just been searching more and keep finding recommendations on webber's and Holley's for MB 280 engines.  For comparison, my 4 barrel Holley 4160  #8007 is 390CFM and I can't find what the Solex is.  From my very rough estimate, a CFM of 375 is required according to this link on a 280 which is 170CID.  What's the Webber's CFM?  It still may be rated close to or lower than that and is probably fine.  A slightly lower CFM rating is not a bad thing according to that link. 

Have another go tuning and search for vacuum leaks I'd suggest.  It's pretty well laid out how to tune it in John's link.  Another tuning hint is to set the idle mixture with a vaccuum gauge connected to the manifold.  Adjust the mixture back and forth until the vacuum measures the highest.  For another read about experiences have a read here mercedesshopforum

1973 350SE, my first & fave



I must say this is turning out as a real Nightmare to me. I have the car for 3 months and I have only driven it for no more than 2 days. At some stage, I really feel like setting it on fire and go to sleep. I remember I specified many times that it is use for a Mercedes W116 280S and the supplier confirmed okay. Yes, one thing that I have noticed is that the new Weber carb is about 1/2 the size of the original Solex and I also remember seeing another local 280S using the same unit........ ???

Really I am getting real sick of this problem and the supplier who ever reply my last 10 messages made things worse. Before I paid, all emails were answer so nicely but sorry things have been completely different after.

What shall I do? Back to buying a SOLEX repair KIT but where????? A lot of suppliers in US do not ship to overseas......Please HELP, I am just a classic lover who want to get the car back on the road.

Here is what I believe have purchased : http://www.redlineweber.com/html/kits/k248.htm


I really don't think there's much difference between the 38DGAS and the 38DGES, after all the parts diagram for the two are the same, eg http://www.racetep.com/webtechframe.html.

Do you get a backfire at all if you plant you foot hard on the accelerator whilst at idle?

I just got back home from work and have to go out again, but I'll try and look into it more later tonight to see if anything else may be the problem.  As I've said earlier, my 280 runs well at high revs but misses at idle very similar to yours and will backfire if I do what I mentioned in the above question.  I've yet to rebuild my carb to check to see if it's the problem, I have all the parts.
1973 350SE, my first & fave


Thx Oscar,

Again I have just spent the whole afternoon talking to different people and have by chance met a guy who drive exactly same car as I do, the previous owner of his car has done a Weber replacement as well and from the looks of it, the Carb is exactly the same as the one I have. NOW, the thing is, his car runs very nice and smooth, so I don't know what is wrong with mine. The worse is the supplier (TOP-END PERFORMANCE) really no longer reply my emails, therefore, I have no idea what he sent me. The car Cold Start and Idles okay now, just that when I REV it, hard or soft, it will go rough and then backfire at about 3,000rpm.



Martin 280s

It's curious to read about your dilemma with the Webber. I have read about swapping the old Solex for any other carb. Most of the reports make it sound like plain sailing. I thought about changing my Solex but, like you inporting things is difficult, decided to perservere and after more fiddling - with the help of the manual - I seem to have it almost where it should be.
The engineers at MB designed the inlet system for the Solex, however crappy it may be, I don't think that another carb will ever be a spot on replacement.
Keep us informed of your progress.
regards, Martin


ESO, I've been looking for ages for info on my own problems as well but come up with zip really.

It's great to hear that you have access to a 280S, already converted and running well.  After rereading the posts, i think a visit back to John's comments about the jet's is in order.  The GAS and GES versions may have different sized jets as John suggests.  Go for a jet kit which I assume won't cost too much.

When I was at my mechanics the other day I asked about my backfire in the 280 and my plans to rebuild the Holley.  He seemed adamant that a rebuild and retune would eliminate the backfire.  But I can't help wonder if it's ignition timing or cam timing.  Sure, you don't have to rebuild your carb but changing the jet's may be beneficial.  John's link has handy advice down the bottom to determine whether jets are too small or vice versa.  Could fuel pressure be a problem too?
1973 350SE, my first & fave


Thank you all for the kind support. To keep you guys updated. I have went for another test drive after I pick up the car from the workshop. Mechanic have now set the idle to about 1200rpm (Neutral gear), I know it is a little high but he said the engine do stall when idle set below 1000rpm.

Anyway,  the car started well at 1st round, rev okay at neutral gear. However when I put in reverse gear, the car started shaking and feel like it was going to stall (even it did not). Accelerating from station, the car will also run a little rough before it goes normal.

In order to check if I have all hoses connected correctly, anyone has a photo of theirs conversion job for me to use as reference?????

Million Thx

john skene

Eric, is it possible to take your jets out and list the sizes for us? It sounds as though you have the standard jets in your carby, which match a smaller capacity engine.