I have a 1967 250S (w108 Chassis) that I am tryint to get ready for my wife. The current problem that I have is that the car wont start when it is cold unless I pour a little gas into the carburetor first (then it starts right up). Once it has started, it idles and drives very nicely...just wont start when cold. A little more information...The distributor was remanufactured by Glenn Ring, I just rebuilt and completely cleaned the carburetors (2 each Zenith 35/40). Before this work was done, the car would not idle at all, now it idles great, choke works. I am thinking that when cold starting, gas just isn't getting into the intake manifold. I am hoping that someone could get me pointed in the right direction. Thank you in advance.

1) With the engine off, and cold, look into the carbs as you open the throttle. (This will require propping the choke plates open.) Do the accelerator pumps deliver a strong squirt of fuel?

2) Have the float levels been set to the high side of the spec?

If the accelerator pumps deliver fuel with throttle stroking, the effect should be the same as manually pouring fuel into the carbs, i.e., enough fuel for engine start.
If no squirt, or only a very weak squirt, the pump check valves/balls may not be seating, or, are missing.

I had some time to work on this problem this weekend. First I checked to see if a squirt of gas was getting into the carburetor...it was, but I am not sure it was a strong squirt, was a little more than a dribble. I tried to find a reference to the check ball valves but was not able to find a diagram displaying them out of the 4 diagrams I currently have...so I am unsure if the ball valves are seated or not. Where are the ball valves located in the carburetor? I have been trying to find a document on adjusting the float level, so I don't know if it is high or to spec. In short, my time this weekend netted no real information. Is there a good diagram/ troubleshooting document for the Zenith carburetors? The ones I have don't show all the parts, or explain the function of all the parts. Thank you in advance.
I did notice that the hard starting problem is not limited to when the car is cold. Once I start the car, and get it up to temperature, if I turn off the car and start it imidiately...all is good. However, if I wait as little as 10 minutes, I need to pour a little gas into the carburetor to get it to start. Just another piece of the puzzle.