450sl schrieb:

Its probably not the cold start valve, which only works for 10 seconds
approximately. Its the cold running phase fuel enrichment, which does
not get temperature or does not react properly.

Signs are sothed spark plugs, black clouds accelerating, fuel smell at
exhaust with engine warmed up.

With that old engine I would try first a new fuel pressure regulator
unit, its rather cheap, second replacement of the cold start regulator,
not so cheap.

These engines are always in danger of rotten o-ring gaskets. That old
material was not designed to work with the modern fuel additives.

I had to replace all gaskets being in contact with fuel, in my 123 280E
after introduction of unleaded euro super.

When I lost a full tank in the night in a italian hotel parking lot, I
have made an end to that story.