we have a 1985 454 with thunderbolt ignition and holley 650 dual feed carburation that gives us poor performance at idle and mid-range rpm. We have discovered that this poor performance (runs really rough) only occurs after the engine has been in operation for an hour or less and it is at full operating temperatures with the choke open. Air/idle mixtures have been adjusted properly, timing is 8deg. BTDC, all ignition components have been tested/and or replaced if suspect, fuel pressures are in acceptable ranges per mfg. specs. Vacuum gauge reveals 15mm Hg with an unsteady needle. Compression test indicates that pressure ranges form a high of 120 psi to a low of 90 psi. Repair or Replace, that's the question. Any insight will be greatly appreciated.
