1967 250 SL Fouling Sparkplugs

[SDave]

I have a 1967 250 SL. One morning I came out and started the car to let it warm up. After about 5 minutes, the engine died and would not restart. I checked everything I could. Finally, I decided to pull the plugs to have a look. They were  very black appearing to be extremely gas fouled. YOu can clean the plugs and it will do the same thing over again. If you install new sparkplugs, it may run for a total of 10 minutes before shutting off and again not restart until I replace the old plugs or clean them.
I was told that was a fuel issue. I have checked everything I know of and it all seems to be in good working order. At the same time, I have never been fully convinced that this is a fuel issue to begin with. But instead I somewhat suspect that it is an electrical problem. I think that this might be caused by a week coil. I am checking that possibility out now.
Has anyone experienced this problem? I have already replaced the cap, rotor button, sparkplugs, and sparkplug wires. I guess I could have went ahead and the replaced the coil also. But I figured I might better stop at this point and look for some advice on this forum. I am hoping and thinking that this problem has occured to other Mercedes Benz owners and can relay to me how to fix this problem.
The engine is a 2.5 liter straight 6 cylinder engine and has a factory stock mechanical Bosch fuel injection system on it. Any solutions,advice, or comments pertaining to this problem would be greatly appreciated. Thank you for taking the time to read this post.

[ja17]

Hello,

It soundl like the WRD "warm running device" is stuck.   This adjusts the fuel quantity from the injection pump when the car is warming up.  If it is stuck rich, as the car warms the mixture will not adjust and the spark plugs will foul out. 

Diagnosis is easy.  First locate the unit. It is on the back and top of the injection pump. (see pic.).  You can use a section of rubber hose or garden hose as a stethescope and listen at the small air filter. When the engine is cold, you will hear air rushing into the air filter. As the engine warms the rush of air will stop. 

The fix is not difficult. Let us know what you find.

[UrbanMyth]

Hi Joe,

I have exactly the same problem with my 250.  Diagnosis?  Stuck!  Would you be so kind and let me know what the fix is please? 

Thanks very much and regards from cold and grey England...

Terry

[ja17]

Hello Terry,

If it is stuck, it can be removed and cleaned up so it works.  Here is an exploded view of it.  Note that two of the lines going to it have engine coolant in it.You must remove the second stage so that the slide valve (piston) can be removed and cleaned.

Take care,