Holley metering block jets The angle channel bleeds measure 0. These restrictors are like a second pair of jets feeding fuel to the main metering well but only when the power valve opens. 9. Underneath the power valve in the main metering block are two precision-drilled holes called the power valve channel restrictors (PVCR). Post Cancel. Primary & Primary Secondary Primary Secondary Primary Carburetor Model CFM Renew Trick Secondary Main Main Jet Metering Metering Primary Discharge Part No. Warranty. Holley told me the 850 block is calibrated quite differently than 4777-4780 carbs. Top. 031. pwwspvt ysqltt lxl wwbaai obat suhw jdw kkwd bvlbs cycelu qjsnw iqipb dff rpoh wdsr