JCB 240 excavator

Hi Guys

I have the following problem on a JCB240 excavator when I stall arm out function my boom raises by itself and I cannot boom down while arm out function is stalled.

I have done the following my pilot lines from the valve bank to the cushion valve have been checked and corrected according to the schematic supplied by JCB agents the pilot lines to the shuttle valve have been checked and corrected as per schematic form JCB agents.

Please guys any information will be greatly appreciated.

Regards

Arnold

JCB 240 excavator