/6 sputters under load

Fuel filter was replaced about a month ago, not sure about pressure. Carb was rebuilt about 6 months ago and float set then. I had issues with it running rich at idle ie; black soot on the drive way. I turned the mixture screw all the way in, which was only about a 1/4 turn, it helped some.

I forgot to mention I'm at 6000ft.

Thanks for the reply, Matt