Rough Running

[ted280sl]

My 1969 280SL runs great when it is cold. Once the engine warms up I experience rough running. The engine seems to miss while cruising at low speed. Acceleration can lead to several misses until the engine achieves high RPMs. It seems to be especially pronounced after I have idled a while for any reason. I recently replaced the plugs, points and rotor. This work on the ignition system did not seem to affect my problem. I have been driving my car for 15 years and typically drive a few thousand miles per year. Many years ago I replaced all of the fuel injectors. The starter solenoid valve by the intake manifold was rebuilt maybe 10 years ago. A few years ago I drained the gas tank and did not find any unusual residue. I suspect my problem is related to the fuel system but, I am not sure of how to proceed. Any feedback would be appreciated.
Thank you,
Ted 1969 280SL

[Benzo]

Im not an expert but the first idea that came to my mind was the Warm Run Device may be stuck. Its something easy to try. Check this info out.

http://www.sl113.org/wiki/Engine/WarmRunningDevice  http://www.sl113.org/wiki/Engine/WarmRunningDevice

[glenn]

Hi, Valves adjusted lately?  Compression?  Sounds a little like burnt valves....

[ted280sl]

Process of elimination. The warm running device seems to be working properly. Once the engine warms up the air intake slows and stops. I guess I need to move onto the valves.
Thanks,
Ted 1969 280SL

[ja17]

Do the split linkage test to see you are running rich or lean at lower rpms.

[ted280sl]

What is the split linkage test? I adjusted the idle fuel mixture years ago. When I made it too lean the RPMs climbed. I then made it a bit richer. I do not know if that meets the "split linkage test"
I have not put fuel injector cleaner in the gas in some time. My next plan to to put some in and see if it improves the problem.
Thanks,
Ted

[Peter van Es]

http://www.sl113.org/wiki/Restricted/Linkage-tour

[alchemist]

If it is running rich, check the cold start device for leakage. If it is leaking, it will keep injecting fuel in the intake.

[franjo_66]

I had exactly the same issue

CSV was sent along with injection pump & injectors for overhaul
So initially assumed it wasn't the root cause for the rough running & overly rich mixture

Well, finally did a check and turns out it was leaking !!!

[travellerdogs]

Cold Start Valve is a simple little device. Take it apart, clean it, make sure the needle is not seized and it moves. Clean the seat up. I did that on mine a few years ago when I was going through the fuel system. Make sure the solenoid is moving by powering it up with 12 volts with a battery and alligator clips. The cold start fuel line is under constant pressure from the fuel pump so a leak iis possibler if the little valve is stuck or dirt on the seat. This is how I remember it.