Two Questions on 190SL

[Pawel66]

I posted those on the 190SL forum, but we have 190SL experts here as well:

Question 1
Assuming I have:
1. Carb with vacuum port with vacuum that can be delivered to distributor
2. 123 Ignition distributor where you can set ignition timing with advance that does not depend on counterweights turning

Are there ignition settings that can be programmed, depending on vacuum and revs, that would work better than 190SL factory settings that were, I suppose, somewhat limited by what the, at the end of the day imperfect, distributor, without vacuum port, could do?

Question 2
I wanted to kindly ask to confirm what I managed to find via "search" function on 190SL forum: the overflow line starts from vents on the top of the float chambers, goes through T-junction (or not on the other arrangement) and goes down, held by clamp, under exhaust manifold, dripping fuel on the garage floor?

Is it correct?

I understand there is no arrangement like on e.g. W113 where there is a fuel return line to fuel tank?

Both questions derive from the fact that my car has Stromberg 175 carb. It has vacuum and I need to hook its overflow fitting somewhere or let it drip on the ground.

I did not say on the other forum that I had a Stromberg as the post would most likely turn into Judgement Day on original set up being the one and only. It may be, but I want to see how the car runs the way she is - so I am kindly asking for information.

[stickandrudderman]

Hello Pawel,
Did you buy that car at a COYS auction in London a few years ago? I remember seeing a 190SL there with a Stromberg. It was rather well done if I recall.
You are correct in that the fuel simply discharges on to the street; you could rig a catch tank if it bothers you.
As for ignition timing, I would simply set it up so you have a max advance that is as per the factory specs and then drive it.
All IC engines run at somewhere between 32 and 38 degress at max advance.

[ja17]

With question #2, the fuel overflow pipe is actually has a dual purpose. First of all it vents the carburetor fuel bowls which is necessary.   Secondly, the factory realized, that if a float needle valve should jamb or get stuck, then the float chamber would fill with gasoline and flood out of the carburetor vents openings and onto the hot exhaust manifold. The long vent pipe was added by the factory for a safety just in case of this malfunction. In the event it did occur the fuel would be carried away from the hot exhaust manifold via this vent pipe and discharged to a safer area. Hopefully this overflow/vent pipe is a part which would never be be used for it's second purpose as an overflow pipe. The long overflow pipe is there "just in case".

[Pawel66]

Hello Pawel,
Did you buy that car at a COYS auction in London a few years ago? I remember seeing a 190SL there with a Stromberg. It was rather well done if I recall.
You are correct in that the fuel simply discharges on to the street; you could rig a catch tank if it bothers you.
As for ignition timing, I would simply set it up so you have a max advance that is as per the factory specs and then drive it.
All IC engines run at somewhere between 32 and 38 degress at max advance.

Thank you!

As for the settings: this is how I will start and, I guess experiment a little in due time, when all the "growing pains" of the restored car will be taken care of.

As for the origin: I bought it from a fellow Club Member here. Where this car came from before that - I have no idea, to be honest. I attach a couple of pictures.

I also have no idea how she will run. Someone spent some time on mods - I have also disc brakes on the front axle (I think 230SL). Brake booster is a factory option, seen on the datacard. The Stromberg and manifold are from W123. The head is with lower compression ratio. So it may be ok, but it may be a fail too.... we will see. I hesitated for a moment if not to go back to original set up, but decided to give it a try. It may be I will be begging everyone to sell me original 190SL head i na few months...

On the picture the overflow line is plugged for now, but we need to change it. On the other picture you see the traces of uneven fight with the steering rod.

[Pawel66]

With question #2, the fuel overflow pipe is actually has a dual purpose. First of all it vents the carburetor fuel bowls which is necessary.   Secondly, the factory realized, that if a float needle valve should jamb or get stuck, then the float chamber would fill with gasoline and flood out of the carburetor vents openings and onto the hot exhaust manifold. The long vent pipe was added by the factory for a safety just in case of this malfunction. In the event it did occur the fuel would be carried away from the hot exhaust manifold via this vent pipe and discharged to a safer area. Hopefully this overflow/vent pipe is a part which would never be be used for it's second purpose as an overflow pipe. The long overflow pipe is there "just in case".

Joe, thank you for help!

I now know how the original set up was done and what were its purposes. Exact purpose of venting of the chambers remains not understood to many, including me...

The Stromberg I need to connect to the car was used in W123 2.0L engine. It had an electric fuel pump, which was pumping fuel independently from engine revolutions as cam driven pump would. So I am afraid we may face the need of handling a typical return flow in my case. The PO hooked the return line right before the fuel pump (which is factory). I do not like it, I am afraid there will be too much air coming in to the fuel flow before the pump. I thought (and please tell me what you think) and my mechanic confirmed that better way will be to run return line (steel line, like the fuel line) back to trunk and hook it with T connector to tank vent line at the filler hose/cap.

Should I install an electric pump perhaps?

Modified post after checking fuel pump type for M115983 - cam driven pump, not an electric pump.

[ja17]

Some electric fuel pumps depend on fuel circulation to cool them. It depends on the type of fuel pump and the operating pressure. Carburetors do not need that much pressure. I know  that the factory Stromberg system with a mechanical fuel pump did have a return line also. Returning fuel directly to the tank keeps the entire fuel system cooled to prevent vapor lock. A lot of carbureted return systems with low pressure mechanical pumps had a return line cut-off to shut down return fuel after the car was at speed to prevent starvation. At speed circulating air took over the task of cooling the fuel system. At idle the fuel return was automatically activated again.

If your using a newer high pressure, high volume electric fuel pump you would probably want to return the fuel directly to the tank so the pump does not overheat and also to relieve the high pressure. Some type of additional regulator or orifice might also be needed in the return circuit. Sometimes just changing the diameter of the return fuel line can be a way to regulate the pressure at the carburetor.

[Pawel66]

Thank you! Very valuable points, thank you for taking time for this education of mine.

[ja17]

You already have two fuel lines on the 190SL. One has a pick up a little higher in the tank than the other. You might consider using the lower one for a fuel return line?

[Pawel66]

We have indeed discussed using the reserve line for return. I was afraid, however, that it would make the reserve line unusable as it might suck air from the return, disturbing the fuel flow while running on reserve (recognising that it would be a fairly rare event). We then arrived at adding one line hooked in the rear to the vent line…