DIY Regulator – need some advice

I have DIY regulator project for my gun. it’s 27 mm inner diameter titanium cylinder. So far seems it’s work, I mean i can set the regulated pressure on firing chamber from 800 psi to 2000 psi by turning the screw in front the body. The problem is when i pull the the trigger ( i set for 2000 psi) regulated pressure goes to 1800 psi, it should be directly back to 2000 psi but my reg need 30 second to reach 2000 psi again. I have tried to adjust the inlet air on piston from 1,5 mm to 4 mm, it doesn’t work..still 30 second to reach set pressure.

here is the pic

http://s1284.beta.photobucket.com/user/ichsanpurwadi/media/regputih_zps7042d03f.jpg.html