Upon cold start up I can see the needle bounce back and forth between 6 & 7lbs. After freeway driving for 45mins. to bring the engine up to running temperature, I pull over to check and find the needle is now steady at 6 lbs.
Any explanation for this ?
This is on a 383ci. with Holley 750cfm., stock Carter fuel pump.

If the gauge is liquid filled and the outside temperature is hot and muggy... that is your answer. Heat and humidity have a drastic effect on liquid filled gauges. This is directly from Autometer's Tech Engineering Dept.

Good luck...

Guage is not liquid filled and tried a different one and same thing happens. Outside temperature was a cool, dry, 60degF. at 9am.

You think it has anything to do with the fuel pump being cold upon initial startup ?

either the supply (pump) end or the demand (needle/seat) end and I'd say the pump. yes might heat it up real good/thoroughly ahead of time (not sure the best way) & see if that smoothes it out