280 SEL two way valve / distributor

[dirkbalter]

Hello,
A little while back I bought a 1970 280 sel, which I am using as a daily driver mainly back and forth to the office.  (It should be similar to a late 280sl).  The car runs nice but had the idle speed set to high. In an attempt to address the problem, I first went through the linkage adjustment procedure to insure everything is good there. After that, I looked into the ignition timing. (The car has transistorized ignition, blue coil with a 066 distributor).
I recognized that the two-way valve had one vacuum line going to the distributor but no line coming from the manifold. The manifold nipple had a plug. In other words, no vacuum was going to the distributor.

I red through the threads in the forum and found:
https://www.sl113.org/forums/index.php?topic=10806.0

Following the advice, I first checked that I have 12V at the valve at idle.
 I don’t.  (the valve itself if I apply 12V, switches fine. Measuring 16-17inHG)
I than bypassed the valve and ran vacuum direct from the manifold to the distributor. (Timing at 8 ATDC with vacuum). The car starts and runs well but I have excessive “pinging” under load at low rpm’s.

I reverted back to my original no vacuum setting with the timing set at approx. 0-2 deg BTDC (750 rpm) and close to 20 deg BTDC @ 3000 rpm.  The car runs relatively good in that set up. However, I am probably losing power and efficiency at higher speed.?
To the experts: how exactly does the valve / vacuum relative to the distributor work? 

What would be the best fix? (I am not too excited about the whole emission system with all its problems as it ages). 
My distributor, also not bad, has a little play between the shaft and the bushing. I was looking into a 123 system.  Am I correct in assuming the 123 would take vacuum direct from the manifold to operate?

Any opinions and help would be greatly appreciated.
Thank you
Dirk

[ja17]

 You should have at least 30 degrees BTDC at 3,000 rpms or your giving up a lot of power and fuel economy. Another option would be find the "vacuum at idle" port on the intake and hook it directly to the vacuum retard on the distributor.  This way when the throttle is opened, the vacuum retard is released and the timing is advanced. You should then be able to set the timing close to spec  at idle and at 3,000 rpms. Power and fuel economy will return.  As a consequence, you will have by-passed the cold idle emission timing feature and the hot running timing feature. No big loss unless you are suffering from some hot running problems. The 123 distributor is also a good option, but you may still be faced with restoring the emission timing features or by-passing them.

[Benz Dr.]

That will work as long as you have the right vacuum port. If you have a constant vacuum throttle body it won't work. One option would be to go back to an earlier version throttle body and then you can use a variety of different distributor options.

[dirkbalter]

Thank you, Joe and Dan, for responding and your advice. I made the mistake to assume the vacuum is highest at idle and as rpm’s increase the vacuum decreases. (I thought I red this somewhere but should have checked that).
I attached a vacuum gauge and as you pointed out, I have constant vacuum going to the two-way valve as well as to the dampener. (Actually, the vacuum increases from around 15in at idle to about 20in at higher rev’s). So now it all makes more sense to me.
Based on what you said, I have the following options:

1)   Fix the problem with the two-way valve that is not actuating and shutting down the vacuum at a certain rpm. This is probably not as easy as it sounds. I am trying to read up on it and from what I understand it involves a couple of relays. Has anybody had a similar problem and has attempted that and have some advice? 
2)   Joe said to find a “vacuum at idle” port in the manifold. I am not sure where to find that or if that can be added? (Probably the easiest)
3)   As per Dan: Replace the throttle body with an older one that has the “vacuum at idle” port. Does anybody have an “older” throttle body for sale?
4)   Something else?

Thank you for your help
Dirk

[Pawel66]

I am sorry to interfere - I am following this thread just for learning... to perhaps better understand (also for myself) what Joe wrote (about directly hooking vacuum from throttle to distributor, with valves, emissions - I have no idea):

Have you studied this: https://www.sl113.org/wiki/Electrical/Distributor

You will find there an explanation related to vacuum in the inlet manifold and throttle - higher or lower, it depends on where you look and where you take it from. In the text you will find reference to throttle body and if you follow this one, you will see the two types of throttle bodies,  as well as ports locations.

If you have late, retard distributor, you then have to have the retard vacuum throttle body with the port down there, under the place where the throttle axel is, more towards the engine (behind throttle as per the air flow). It is a short piece of metal pipe, about 4-5mm diameter, sticking out of the housing. On the picture you have the rubber pipe connector installed on this pipe and the white plastic line coming out of the rubber connector.

In this set up (vacuum retard throttle and distributor) you have the biggest vacuum after the throttle at idle (throttle closed, suction from engine). As throttle opens, vacuum gets lower and releases retard from distributor that advances the timing. Idle = high vacuum = retarded timing.

Sorry if I am messing anythign up...

[dirkbalter]

Hi Pawel,
Learning myself.
In my case, (70 280 sel or other late 280 sl’s) the throttle body vacuum is constant. Earlier throttle bodies (except very early 230is) provide max vacuum at idle and release vacuum as rev’s increase.
The vacuum release (70 280 sel or other late 280 sl’s) is done thru an inline valve that turns the vacuum of at a certain rpm (2500rpm?) to provide proper advance. My problem is that I have no voltage going to the vale at any rpm. The logic in triggering the valve is part of a reduced emission scheme that was added in later 70-72 cars. 
That’s why it was suggested to use an earlier style throttle body that does not use the valve and vacuum is connected directly to the distributor.
(That’s my understanding, please correct me if I am wrong)
Dirk

[Pawel66]

ok, I do not want  to mess the logic here, sorry.

I am not sure where the vacuum port should be on the throttle body to work with the latest distributors - so far I thought they were with retard type port location on throttle body, but I do not know this.

There is this section on Emission Control in the Manual: https://www.sl113.org/wiki/Electrical/EmissionControlSystem

It explains how it works and what controls the valve, but I am sure you already studied this.

[dirkbalter]

Thanks Pawel
was studying it as we speak. I think all later type distributors including mine are of retard type. My problem is that the distributor will not advance properly due to the two-way valve not turning off the vacuum.
 

[Benz Dr.]

Hi Pawel,
Learning myself.
In my case, (70 280 sel or other late 280 sl’s) the throttle body vacuum is constant. Earlier throttle bodies (except very early 230is) provide max vacuum at idle and release vacuum as rev’s increase.
The vacuum release (70 280 sel or other late 280 sl’s) is done thru an inline valve that turns the vacuum of at a certain rpm (2500rpm?) to provide proper advance. My problem is that I have no voltage going to the vale at any rpm. The logic in triggering the valve is part of a reduced emission scheme that was added in later 70-72 cars. 
That’s why it was suggested to use an earlier style throttle body that does not use the valve and vacuum is connected directly to the distributor.
(That’s my understanding, please correct me if I am wrong)
Dirk

I'm glad you noticed that. It is what I was referring to as there are three different throttle body types used on our cars.

[dirkbalter]

I'm glad you noticed that. It is what I was referring to as there are three different throttle body types used on our cars.

Yup, and thanks again. Contrary from what my wife says, I am a good listener. (I just bought a 68 throttle body on e-bay. In case plan A does not work).

[Benz Dr.]

That's one way to sort this out but you will likely need a 051 distributor to go with it. Your 066 won't work.

[dirkbalter]

That's one way to sort this out but you will likely need a 051 distributor to go with it. Your 066 won't work.

Dan, I was wondering about that. I actually have an 051 from my 230 which will not be ready for another 1-2 years probably. The centrifugal curve seems to be the same, but my 066 has 10deg more vacuum retard. Is that why you are saying that?
As mentioned in my earlier post, I might bite the bullet go for a 123 system. That should work?
Thank again.

[Benz Dr.]

You match the distributor to your throttle valve. 051 will have a different curve but will still work as required.

[dirkbalter]

Just a FYI and a thanks to the guys that guided me through that.
I replaced the throttle body with an earlier (68) one that had the max vacuum at idle port.
I replaced the “66” with an rebuild “51” distributor.
I removed all the later ignition components/relays and for the moment running 12 V straight to the blue coil. (I have a red coil with ballast on order).
The car runs very well. Idle, starting, power. It feels like it could use another gear at around 65-70 mile/h but I believe that’s normal. No more “pinging” or “nachdieseln”.
One question though. What exactly is the function of the “vacuum pot” that is attached to the throttle body and operates the throttle flap? (picture, bottom center ) I did not install it and do not seem to miss it.
Thank again

[ja17]

Certain years USA cars with automatics used the vacuum pot to increase idle when the car was placed in a drive gear. The constant speed solenoid was either not used or used with the AC if equipped, to boost idle when the AC was switched on. A "slip-joint" (on the linkage between the intake and cross over rod) was used in conjunction with this dashpot. When the car was placed in a drive gear, vacuum would decrease and extend the dashpot which pushed open the venturi valve. The slip joint allowed the linkage to be moved easily since the dashpot only moved the venturi lever and not the entire linkage assembly.

[dirkbalter]

Joe, thanks. My set up is exactly as you describe. What I didn’t know or don’t understand is the vacuum decrease when placed into gear. What makes or why would the vacuum decrease when placed into gear?