Need help--falling fuel pressure

[DFRESH]

Just put a new system in the car---750 Holley DP (Proform), Ricks Tank, -8 hose, mechanical pump (Holley 9 pd). I am not running a regulator. Here's the story---on the guage (right at the carb) it started off strong right at 9--but as the car got warm, it was dipping down to like 3 pds.

Now, I am used to FI--my pressure on the race car never moves---well some but only on a pass and very small movement at that. This is idling and me trying to tune the carb a bit. I know heat can affect the pressure, but down to 3 pds? I took the guage off and checked for debries---nothing. After it cools down a bit--it will jump up a few pds--but drop back to 3. I haven't dealt with a mechanical system in quite awhile---one other thing--Hector told me to block off the vent on the tank, and vent through the cap--he gave me a part # to use. Do I need a regulator with this mild of a system?

Doug