engine dies after full warm up (transistor ignition)

[Iconic]

I bought my car in a non-running condition 2.5 months ago (several/many years of storage).
I've done a lot of things. Disposed of old fuel, flushed tank, cleaned screens, new fuel filter, new fuel lines, new fuel pump, disassembled and cleaned WRD and checked WRD thermostat. My FIP mixture rod moves freely. My fuel circulates back to the tank nicely (even when I lock jaw the smaller pump output that goes to the "T").
Now the engine starts great, idles great until it warms up.
I was having a great maiden voyage until it died.
It will idle in my garage and I will keep it running at about 1500 or 2000 RPM, then it starts to stumble a few times for about 20 seconds, then it cuts out completely. From cold start to death takes about 7 to 15 minutes (I haven't really timed it). It is very predictable and does it every time I allow it to warm up. Once it dies, it might re-start one or two times, then it is completely dead until I leave it for a while.
I have taken the WRD air intake out of the equation just for experimenting. I put a rubber stopper in once it gets up in temp. I see the mixture rod moving in the correct direction so I believe the thermostat is working properly on the WRD. I have put it in boiling water and it moves the specified 6 mm or so.
I have tried to read everything about this on the site.
I have the same symptom before and after installing new points, plugs, cap, and rotor.
The symptom leads me to the switching unit (transistor box), but, I have done the appropriate tests and it passes when it is cold and after I have a "death" experience when warm. I've done the test procedures several times (many). One time, it seemed like I had 0.15V at the switching unit side of the 0.6 ohm resistor with the points open (when I am supposed to have 0.0V). But, the reading went away immediately so I don't know if it was just a fluke.
What do you think?
Have I missed something?
This site is amazing. I would not be able to own this car without this site ... I am really chomping at the bit to drive this thing!!
Thank you.

[hands_aus]

What about the COLD START VALVE (CSV) on the inlet manifold.
If it is leaking you will have a very rich running engine.

There is a HOT IDLE test...
disconnect the link rod down to the inj pump.
increase air supply....if rpms increase more than 1-200revs mixture is too rich.
increase fuel supply ....if rpms increase more than 1-200revs mixture is too lean.

Have you checked the colour of the plugs or exhaust pipe?
if plugs or exhaust pipes are sooty it indicates too rich
if plugs or exhaust pipes are white it indicates too lean
a nice silver gray exhaust mixture is ok

[Iconic]

Thanks for your response.
I think I'm OK with the CSV. I took the little bolt out of the side of it and no fuel comes out when running warm. Also, the sudden event I am talking about probably isn't caused by rich running. The engine just cuts out at a certain point. Please tell me if I am wrong.
So, this also applies to the hot idle test. The suddeness of it does not imply a slightly rich or lean situation. I haven't driven the car and it doesn't run hot for long, so I don't know if plug reading would give me any information.

I now realize one basic thing. Once the engine goes into this no-run mode, I will see if I have spark at that moment. Up until now, I've been testing the switching unit (transistor box) at that time. But, I need to get more basic. Once it warms up and dies, I will determine if I have spark at the plug and fuel.

By the way, both resistors are hot to the touch (maybe 150 degrees F). Is that normal? or a clue of any kind?

[Naj ✝︎]

The problem I had was a clogged return line in the fuel tank.
The fuel was not circulating and would heat up and cause a vapour lock and the engine would die. Let it cool for 20 min or so and it would run again.
When it cuts out, try bleeding the fuel from the bleed screw on the main fuel filter housing with the ignition on and fuel pump running. you may feel cold fuel running out, then warm fuel and then cold again. Then try a restart.
Mine would run when I did this.

naj

[Iconic]

Thank you Naj, you could be right because I now believe it does have to do with the fuel and I need to "switch gears" away from the ignition. I thoroughly check the spark. While warming up I kept a timing light on and I monitored the negative side of the coil for voltage. They both never quit as the car was dying. then I pulled a plug wire and stuck an extra plug in it and I still had spark. So, my ignition is fine (I believe) and I now need to reevaluate the fuel system.
Although, I have checked my fuel circulation back to the tank by clamping the extra fuel line out of the pump (before the "T") and therefore forcing all the pump's output to the front of the car and the FIP and back to the tank. I sat in my trunk and looked through the little sender hole and verified the fuel was making it back to tank.....
So, now I have to go back and study up on the fuel system unless someone can give me the answer I've been trying to find... the key to my driving pleasure. I'm confident it will be worth it once I get to the open road.
Mark

[wwheeler]

I believe the CSV leak test is done with the engine NOT running but with the fuel pump running. When the engine is running, it pulls a vacuum through the bolt hole and any leaking fuel just gets sucked into the intake. Am I correct?

[Iconic]

wwheeler, yes the test is done with the engine not running. I misspoke and I probably meant that I had tested it when the car was cold and was warm. But, just to be safe I re-tested and there is not leak. Then I tested the whole CSV / TTS system and all is good.
I started this subject in the electrical Forum because I suspected the ignition, but now it should really be in the Fuel Forum.
Naj, you were right on.
The bottom line is I had a restriced fuel line going back to the tank (the return line) just as so many others have had (and Naj too).
I blew out the line and now I have much better flow. AND THE CAR RUNS.
I drove the car yesterday for the first time since I bought it. 12 miles with a bunch of restarts and idling.
I am thrilled. Of course, I have plenty of more work to do on the car, but at least I can now drive it !!!
By the way, I did take several flow measurements. I will make a post in the Fuel Forum with the data.
THANKS for your help.
(now I have to change my Avatar (one with the car off of the flatbed))
Mark

[Naj ✝︎]

Good to know you're getting sorted 

naj

[tonyfern75]

What about the COLD START VALVE (CSV) on the inlet manifold.
If it is leaking you will have a very rich running engine.

There is a HOT IDLE test...
disconnect the link rod down to the inj pump.
increase air supply....if rpms increase more than 1-200revs mixture is too rich.
increase fuel supply ....if rpms increase more than 1-200revs mixture is too lean.

Have you checked the colour of the plugs or exhaust pipe?
if plugs or exhaust pipes are sooty it indicates too rich
if plugs or exhaust pipes are white it indicates too lean
a nice silver gray exhaust mixture is ok

Ive done this test and find that I cannot get my engine to idle well unless I keep it rich enough so that when the linkage is disconnected and I open the throttle flap I can get it up to 1500 RPM's. This doesn't seem right. Is it worn valve seats? I've got the hottest ignition I can get with points via the RED Bosch coil and the recommended NGK's My plugs look good whenever I pull them. Is this the exhaust valve ball stud problem? Any advice would be appreciated.

Tony
1967 230 SL automatic

[ja17]

Hello Tony,

Make sure your ignition timing is correct and your engine linkages are set correctly (engine linkage tour).  If it is ok, it sounds like your idle mixture is a bit rich, try adjusting the idle thumb screw on the back of the injection pump a click or two (with engine off).