Tom, with the drive pulley's speed, being constant, increasing the diameter of the ps pulley will make it turns slower, per engine rpm, and reduce the pressure, in theory. But, you may have a pressure valve, so it will reach it's working pressure, later.

If you have not had this problem before and it just started acting up,you may have a pressure/relief valve plugging. The viscosity of the ps fluid may be old and has thickened in viscosity.

I would change the ps pump-fluid, to new ps fluid, and see what happens, before changing the pulley diameters. Paul.

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