I have W114 with M130 6 cylinder with dual Zenith INAT 35/40.
I didn't drive the car a lot since o bought it (was brought on flatbed to my house) so I can't comment too much but it felt at least ok with enough power and maybe needed some carb adjustment.
In the last couple of months because of the weather I worked mostly on the interior and would start the engine once in a while no issues.
What I have done:
1. New engine oil (rotella) and oem filter
2. New tranny oil and filter
3. New differential oil
4. Bosch spark plug wires
5. Bosch platinum spark plugs
6. Changed all vacuum connectors on the engine bay
Here is the link to the cables
Previous owner installed Crane electronic ignition.
I have checked the second membranes and they look good, the second from the front feels much more worn than the first. (Picture attached)
I have changed the gas, cleaned the carbs with carb cleaner and added cleaner in the tank. The car and the rest of the components are in pristine condition.
I have also adjusted the gap on the plugs to .8mm and that made it worse.
When I removed the new plugs I noticed
plugs 1, 5 and 2 are grey and dry as they should be.
spark plugs 3,6 and 4, specifically 3 were black and wet, like the gas is not burning properly.
Another thing I noticed is when i remove cable on cylinder 5 for example you can hear the engine idle change but when i do for cylinder 3 there is no change which leads me to believe cylinder 3 is not firing.
Needles to say the engine is out of power and sounds like garbage.
Starting the engine cold or warm is no issue at all.
I don't know if I have enough information and I greatly appreciate any input on this problem.
I also found few wires not connected close to the crane device.
You can see marks on the hood from the carbs back firing.