I have an older Curtis compressor which sat idle for several years. We recently had the motor cleaned out and adjusted. When we hooked it back up it ran like new. Only problem is it gets to 75 psi and want make anymore pressure. The pump keeps running and it doesn't appear to be leaking. Seems to be bypassing somewhere. Its around a late 70s model. Any ideas. Its a 3 HP I was told with a 30 gal tank.