One port :low pressure on KE jetronic fuel dustributor

[d333gs]

I have one port (not injector or rail) with low pressure on KE jetronic fuel dustributor causing rough idle, all other ports are good. Pressure builds with increased RPM

Any thoughts on what happens to cause this?
(1986,560 SL)..

TIA

 

[ELGRINGO]

We had simular fault with sl280, turned out to be metering head at fault, rust etc, in head.

 

[d333gs]

Thanks. Barrel with metering slits ?
were you able to clean it or did you replace it?