is it acidic, or sour? Could be the beans, but more likely its brew temp. I dont know specifically what temp the ikon typically brews at, but the 800 (a model up from the ikon) the brew temp is arround 88-89C (which is much too low). To ramp if up, you can kick it over to steam and let that go for a few seconds, this gets the thermablock up to 103, and then insert the pf and kill the steam and start extracting the shot.
Try this, and if the shot now tastes burnt/bitter as opposed to how it was tasting, its likely the brew temp is the issue. Now to get the optimal brew temp play around with timing, its hard to be 100%accurate without a k-type thermocouple but let taste be your guide. You might need to wait 1 second after disengaging the steam before kicking into extraction or 10 seconds (or 1.5 or 3, or 5sec etc).
Let us know if this helps at all