troubleshooting bosch K-jet

[mabbonizio]

Hi Folks,

I've posted on w116.org but thinking I might seek some opinions here as well.

I think I've scoured every corner of the internet for K-jet information but perhaps I've missed something.

First let me say my car has new Spark Plugs, Dist cap + rotor, injectors, seals, refurbished fuel distributor, new fuel pump + filter , and a clean fuel tank.

My 77 450SEL starts fine sometimes and rough other times. When it's warmed up and has been running for a while I can shut it off, run out to a store and come back and it will fire right up.

If I let it sit for a couple hours it will start rough and chug for 5-10 seconds then even out.

Sometimes when its cold (sitting overnight) it will start fine, other times it will start and chug.

Now, if I unplug the blue plug on the fuel distributor before starting (I believe this allows the fuel pump to constantly run) It will fire right up. This leads me to believe there is a loss of pressure in the fuel system.

When I first start the car from cold, it makes a funny whirring noise for about 5 minutes.. Is this a normal air recirculation noise or is this a symptom of something being wrong?

Lastly, at approx 2,500 rpm (light throttle, just enough to cruise and hold speed at say 60 mph) the car seems to have a slight hesitation. This has gotten MUCH better as I've driven it a couple hundred miles but it is still present. Any ideas?