I recently had my intake on my LB9 off to replace leaking gaskets at the base, and while it was off I modified my fuel pressure regulator per some instructions off this site (can't remember where though) by drilling a hole in the endcap, brazing a 1/4" nut to the outside and putting a 1/4" bolt in to make it adjustble.

Before I had 39-40 at idle, and with the vaccum disconnected I had 43 psi. I can back the screw out and have the stock settings, but if I turn it in enough to raise the pressure more than 5psi the guage spikes all over the place- now I have no problem with it running and in fact with the setting at 48psi w/o vaccum the car cold starts much better. I have not done any G tech or track passes to see if the raised pressure makes a difference but is it normal for my home adjustable regulator to cause such pressure spikes?

 

May guess is You need something between the end of the bolt and the spring cap to keep the bolt from forcing the spring from turning which will also cause the diapham to twist which it isn't designed to do, or round and smooth the end of the bolt so that less area comes into contact with the center of the spring cap just don't make it a sharp point.
Use a vacuum pump to check for leaking when you turn the bolt, did you use a coarse, or fine thread nut & bolt?