The Cal-look Lounge

I have trouble with my fuel pressure... It seems it starts to fluctuate when the car has been driven for some time, like 1/2-1hr.
Have tank - fuel pump in the front - copper tube trough car - filter king regulator - pressure gauge - "t" fitting - carbs.
The carbs are italian ida´s with original fuel fittings, the pump is the one in the link below. 8mm hoses and copper tube all the way.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=CRT%2DP4259&N=700+4294839053+400415+4294836965+115&autoview=sku

I´m running out of good ideas, help appreciated!

liquid filled gauge? If so it will "show" different readings when hot than when cold.
I got rid of my liquid filled back in the 90's because of same quandary. Of course, my non-liquid filled VDO gave me hell a few months back too ::)

It is liquid filled but it should not fluctuate even if it got hot? It´s mounted high on the firewall so I don´t see it get that hot?

Mine was up high too, and when the engine compartment got hot it would read much lower than when cold.
So I would turn it up and engine would bog and bumble and flood.

Get a non liquid filled.....they're cheap. It will show consistent psi

Have you got a decent breather on the tank? Just a thought: the engine runs for a while, drains some of the fuel, creating a slight vacuum in the tank, causing the pump to cavitate and lose pressure... Leave the car standing and the vacuum disappears. Run the car again, and the cycle repeats itself. As I say, just a thought.

I have a Swedish car who originally had a "security" filler installed. This one has a separate breather, but a small one. I´ll try to run it without the cap and see what happens. Thanks for the tip!