> Could there be a limit of the ide powermac port [...]?

The on-board PATA controller of PowerMac G4 up to and including Quicksilver (2001) only supports LBA28 (ATA-5), which means 128 GiB maximum for drive size. Quicksilver (2002) and later models support LBA48 (ATA-6), which means 128 PiB maximum. This doesn't seem to be the issue you're facing though, as you say your 240 GB SATA SSD works well via the adapter (which seems to remedy the LBA28 restriction), if I understand right.