Accessing the mixture adjustment screw

[Feather535]

Well, the 280 SE failed the California smog test.  CO and HC are quite a bit too high at idle, but ok at high RPM. 

That was with a warm engine, new fuel and a recent oil change.  The warm control pressure is correct, but the ignition timing may have been retarded by a few degrees.  I've since reset it.

What else to check?

I'm thinking I may to adjust the fuel mixture, but there is a slot-head screw in the collared opening on top of the FD and it's very tight.  Is this normal?

[ramiro]

Just to be sure , the opening is between the FD and the Air Meter plate not on top of the FD.
Most likely somebody closed the opening with a standard screw so you have to unscrew the screw and then you should be able to adjust the mixture with a alan key but be very carefull, one turn and your engine won't run anymore and it's also best to measure the mixture while you are adjusting.

[Feather535]

Just to be sure , the opening is between the FD and the Air Meter plate not on top of the FD.

Yes, that's the one.