280S won't idle...

[Nabstud]

Took the car on a 60km drive on Friday night, ran like clockwork. Stopped and started the motor a couple times on the drive and it was running perfectly. Got home and put it in the shed where it was idling like a sewing machine.

Started it today, cold started like it normally does and I let it idle for a few minutes before I was to drive off (as I normally do). I gave the accelerator a quick little jab to turn off the auto choke as I do and then it just died. It starts again no problem but will die within a couple seconds if I don't give it some throttle. Even with light throttle it is now running rough. If I give it moderate throttle it revs clean and smooth as per normal, anything below about 1500rpm is starts carrying on and will die if I don't give it some throttle. Haven't go a vacuum tester yet so I just checked all the vacuum pipes and sprayed everything with carby cleaner and it made no difference.

It also now has a manifold or exhaust leak up neat the motor, noticed it was a little louder on throttle towards the end of my last drive but not enough to worry me. Now when it is revved there is definitely exhaust leakage near the motor.

Any ideas? Up until today it has been running great, even the cold start today was like normal. I've done about 500km in it since I've had it with normal running.

Solex carby buggered? I thought it may give symptoms before causing such an issue.

[Bartman4800]

Have you checked the condition of your fuel filter?

My guess is, that some dirt entered the primary circuit of your carby, or some accumulated dirt has come loose.

I used foaming carby cleaner before, and got great results.

https://www.nulon.com.au/images/files/p ... PB-AIC.pdf

If a jet it clogged, you can try blowing some compressed air into it.


Bart

[Nabstud]

Are you talking about the filter in the carby(I think there’s one in there)?

[Bartman4800]

I did not even think of the strainer in the carby.

There must be a filter between the fuel tank and the carburettor.

Other than that, the float needle could be a bit buggered too, but it seems your car is running lean, not rich.

If I was you, I was gonna get under the car and ensure all fuel hoses and filters are of good condition.
A perished hose could suck in some air, and cause a fire further downstream...

Bart

[CraigB]

First gut feeling is to take it easy on looking for solutions, given how well it was running before putting it away. If you start jumping at lots of things it can get confusing, so tempting and been there myself, hence the comment.

First thing with the exhaust, get a bit of plastic tube in your ear and move it around where the sound is coming from exactly. Manifold to head face should be metal crush gaskets and unlikely to burn out, so just nipping up the bolts a bit might work, but make sure plenty of penetrating fluid first - perhaps try to undo a bit first before tightening and really importantly, don't get heavy handed..... having just had to get 3 broken studs out of my M110! But if you can get threads free, you can probably tighten enough to seal it up.

But the biggie for exhaust leaks on the RHD M110 is the crazy y piece that joins the manifolds and then splits again later. The Y piece is famous for cracking. That's why I said about the hose to isolate where the leak is. Your looking at long term ownership, so I would suggest doing what i had done to my earlier car. A clever exhaust guy can replace the y pieces with two tubes - there is enough room to get them past the steering box. The other alternative is to get manifolds from other M110, I think W126 and W123, that have two rear exit manifolds and one pipe goes down firewall and other sort of under the steering box, but and exhaust place will work it out.

Its a shame if that is the case, having just got the car and had it checked out, used it like it should be etc..... but the other way of looking at it is that its just a matter of time before its a problem. People have welded them up, but I reckon its an inherent problem and performance wise, seems crazy to me to cram the gas together and then split it about again. Of course LHD cars ran the two pipes to the rear, but I guess MB considered not enough clearance for their liking with the steering box there. But I sprinted my car and drove it flat out and the pipes never touched.

But with the idle, I would take it on a decent run (after having a good look for intake leaks) and see if it settles it. Also I would nip up the carby base nuts, then maybe check the gasket. Check as you have with aerostart or something around there maybe too. What I am getting at is that the solex has a reputation that it can warp the body and maybe that can change as it heats up and expands everything. Cooled down and after the long run, maybe warped a little. You could dismantle and sand on a glass plate with sandpaper on it, but I would start in the order suggested, just tightening the bolts a little, but also look to see if disappears when warm - thinking how well it ran after your run.

Also of course check any of he manifold nuts and gaskets, vacuum as you have, but my thinking is that it is expansion related with heat and not sat a blown gasket or vac line split - because it was running smooth before cooled down and then noticed

That's my brain dump for tonight, but not disputing other thoughts from Bart.

[Nabstud]

I went under the car and followed the fuel lines, nothing amiss nor did I find any filter, maybe it's near the tank? I took apart the filter at the carby and it was clean, I gave it a good dose of carby cleaner to be sure. (had a slight mishap with a coolant hose breakage )

I sprayed it all again looking for leaks with no luck but I forgot to do the manifold/head area. Will try it next time. I also checked all the mounting bolts and screws but they were all tight.

Good idea with the hose to find the exhaust leak, again on the list for next time. I did see a little bit of black soot between the manifold and exhaust joint, will check it with the hose.

Also undid the idle screw (after first tightening it and counting the turns - you learn that one quick haha) and blew it out and gave it some carby cleaner, still no luck. I'm not touching anything else haha!!! You are right, it seems like a component failure or a sudden big change to vacuum to go from running perfectly to not idling on the next start.

I did a bit more testing with the throttle, if I hold the throttle steady at 1500-2000rpm it barely holds steady, but if I let it drop to idle and give it a tiny rev every second it will sort of smoothly sit around 1000rpm. Looking into the carby plenty of fuel is being squirted in there. Revving anything over 1500-2000rpm is smooth and strong.

[brycedunn]

I went under the car and followed the fuel lines, nothing amiss nor did I find any filter, maybe it's near the tank?

I've not had a carby M110, but on the fuel injected units the filter is at the back next to the fuel pump. There is a shield to protect it from road debris.

I also had sort of similar symptoms with a 250SE when the fuel tank was low. There was a blockage in the swirl pot in the fuel tank. When the level was above 1/3, no problem.

[CraigB]

Given what you have done and running strongly up higher, I would just take it for a good run, get it hot and see what it does then. If it idles nicely like it did the night before you put it away, then you can be pretty sure you don't have to chase filters, jets etc - that was my thought that is was less likely that overnight and at idle, all this crud jumped in there and more likely that something had heated up and cooled down just that little bit more, a seal broken etc. and allowing that intake air leak somewhere. That was where my thinking was at anyway.

Also a seized nut to a stud will feel tight. Undoing and tightening again will give a better indication... but take care with how much force, don't want to break anything. But if you can see soot lower, chances are it is down there and not the manifold to head. Manifolds to Y is a tapered metal joint and no gasket (well on the one I recently pulled off) so unless loose, chances are there is a split around there somewhere. ie. not gasket to be leaking.

[Nabstud]

Problem solved!

Short answer, blown fuse #4 and pitted points.

Long answer. After doing some research last night the thing that I kept reading was "check the basics". All I had done so far was check fuel filter, check hoses and carby for vacuum leaks, check screws/bolts are tight and check the front idle screw (I think). So I decided to start from scratch. All hoses connected, no wires loose etc etc. Then I found #4 fuse blown. This does the electric choke, temperature gauge, as well as numerous other things including reverse lights, which is where the reverse camera gets its power from. I disconnected the camera and now the fuse doesn't blow. This didn't solve the idling issue but it did make it start much easier this morning. Hmmm, it was working fine up until now, maybe I pinched the cable while doing other work on the car, but the camera was working until today. Good excuse to get rid of the reverse camera... Come to think of it there were 2 white fuses in the glovebox (8A, same as the blown fuse) and the blown one was new looking, maybe this was an intermittent issue the previous owner couldn't find?

Then I started on the ignition system. All looked good until I got to the points. I went to measure the gap but I couldn't even get a 0.05mm feeler gauge in there, even though I could see them opening while rotating the motor. When I took them out there was a tiny bit of pitting that I couldn't see while in situ. I used some fine emery paper to make them smooth again and re-installed and he fired up like a new one. Checked the dwell angle (36°) and timing (7°), a bit of fine tuning got them within specified ranges. It was idling a bit high at 850rpm so I dropped it down to around 750rpm in park.

I still don't understand how it was driving and idling perfectly one day then terrible the next? One of life's mysteries.

Moral of the story - check the basics!

[CraigB]

Thanks for feeding back. From the original post I didn't get that it was hard to start, not that I would have thought of that fuse, not realising link to an electric choke. I usually think of points breaking down at revs too.... but there you go! As long as it is working. If you keep having points problems, it could be the condenser and also there are discreet breakerless ignition units to be had.

[Bartman4800]

+1 on the condensor

If it is cactus, it starts sparking hard over the points and they wear out in no time.

Time to invest in an electronic ignition! (I am surprised this does not have a factory one actually)

https://www.benzworld.org/threads/conve ... 3.2422697/

https://www.123ignition.de/123-ignition ... -usb.aspx

Regards, Bart

[Nabstud]

I suppose I should have said smoother starting than easier, it has always started no probs. I also thought points affected high revs too, this ones over my head...

The points looked new but the condenser looked pretty old so your idea of electronic ignition sounds pretty good. Having some fun with it at the moment though, bringing back memories servicing my old datto. I reckon adjusting them every couple months might get old though!

[Nabstud]

Found the reason for the reverse camera sometimes blowing the fuse. Whoever installed the cabling ran the monitor cable under the carpet and through the drivers seat rails somehow. This was all good until I started playing with the height adjustment, looks like they somehow ran the cable through the rails and I seem to have run over it! I just pulled out all the reverse camera wiring and problem sorted!