1979 280E Runs Rich when Hot

[Tony 12]

Some time ago, my 280E ran rich when hot, I pulled apart the Warm Up Regulator, cleaned it out etc and it was fine.
The same symptoms have now returned.
Today I replaced the fuel distributor, warm up regulator and cold start valve off a known good car, and the problem persists.
Once it hits 87 deg. it idles not too badly and will rev with no load, but as soon as you apply load, it blows black smoke, stalls and won't restart. Let it cool for a while and it's ok again.
I think there's also an air bypass thingy under the manifold but that only serves to up the idle speed when cold. Correct?
Can anyone bestow their infinite knowledge upon me?
Thanks in advance for any advice.

[93_300E2.8]

My guess would be that the cold start is stuck on.

[cheapold280ce]

Check out these manuals and see if you can fiqure out what is wrong. One has step by step troubleshooting. You will need to setup some guages and recreated the problem and see what the pressures are doing.

http://w123gassers.smfforfree2.com/index.php/topic,408.0.html