Chevelle has been sitting 10 months while engine was being partially rebuilt. Gas tank was about 3/4 full. Yesterday, I finally started for the first time. Started instantly. While at idle, fuel pressure was 7 PSI. Maintained 6 PSI while at 2000+rpm. As engine idled for approximately 20 minutes to bring to operating temp the fuel pressure dropped to 3 PSI at both idle and 2000+rpm. After another 10 minutes the fuel pressure dropped to 0 PSI. Even at 0 PSI engine maintained idle for another 10 minutes and never had any apparent gas starving symptoms albeit I never went much beyond 2000-3000 rpm. What is going on? Could the fuel lines/filters be clogging? What testing should I do find cause?
-396 CID
-Edelbrock 750cfm
-Edelbrock fuel filter between pump and carb
-Liquid filled pressure gauge after pump before Eddy fuel filter
-Holley mechanical fuel pump (not sure pump rating)
-No return line, non-vented gas cap, vented tank (looks original and very dirty) I did pop the gas cap off while at 0 PSI and didn't appear to have a vacuum.

Liquid filled gauges read lower the hotter they get. Try temporarily mounting the gauge remotely (away from heat) to verify. If this works, drain the fluid from the gauge and do not put the plug back in the gauge. Not having the fluid in the gauge may cause the needle to bounce more than before but at least it won't be effected as much by temperature.

Liquid filled gauges read lower the hotter they get. Try temporarily mounting the gauge remotely (away from heat) to verify. If this works, drain the fluid from the gauge and do not put the plug back in the gauge. Not having the fluid in the gauge may cause the needle to bounce more than before but at least it won't be effected as much by temperature.

Thanks for the advice. You're spot on! After several periods of cooling down and then retesting the pressure gauge readings drop as engine compartment etc warm.

Will try non liquid filled gauge.

Thanks!