[greglepore]

Doubt its the burrs. You can always clean them as a start.
35-40 seconds should be ok, but is on the long side. Long shots do tend to be richer but can quickly veer towards sour.
You're using a triple basket in a bottomless?
I would check your brew temp with a thermometer in the group or cup. Pressurestats can drift over time and require adjustment.
Sour is usually overextracted, so I'd aim towards a lighter grind and tamp and shorter extraction.
Also, I'm assuming that the brewpath and portafilter have been really cleaned at some point with a Caffiza backflush and a soak of the portafilter other than a simple rinse backflush.