Orifice Valve Not Working?

[FisherKing]

I have a 96 Evinrude 28 HP. I've just rebuilt the carb and got the engine running again. Initially it wouldn't run. I then tried removing the orifice on the top cover and it fires right up and runs (idles in the driveway anyway) just fine.

If I put the orifice (intermediate no. 55) in only half-way then the engine runs rough.

I'm wondering how this thing is supposed to work. It was screwed all the way in when I took the carb apart and left it as was.

Is it possible that this thing is bad somehow? I've made sure the hole is clean and clear and no difference in the way it starts (it will start and run without the orifice).

I guess it would help to know what this thing does for the engine, maybe help me figure it out.

Thanks for any ideas.

[boats.net]

Possible still have a p***age plugged up in carb.