Basic Info: 66-67 Holley introduced the 3 Barrel for public consumption. In 1964 Chrysler had Holley build them a carb list #3085 for their Nascar Hemi motors and this was the Holley 3 Barrel. There has been no info as to tuning issues with the Nascar version.
Now, 66-67 with the introduction of the 3 Barrel to the public, some how emissons became involved and the carbs were tuned to meet those standards. In this case the Emisson standards seem to go towards leaning these carbs out. I don't know if Holley ever tested these carbs or if the changes were just done on paper.
For such a large carb Holley had installed .040" PVCR's in the primary metering block #5615 to lean the primary out to meet Emission Standards, resulting in a flat spot, the initial fix was to go larger jets which caused it to run pig rich, so now this is just the primary issue, now the 2ndaries were also lean and at wide open throttle there was a substantial bog from being to lean, an idea came up for a fix, which was to remove the vaccum canister and make the primary and secondary one to one, so gears were made, and a primary shooter was extended to the secondaries for a fuel shot to richen up the secondary during the lean peroid during blade opening.
Previously, everything done were just Band Aids and didn't NECESSARILY fix any of the issues.
The Nascar's 3 Barrel metering block #4328 came with .093' PVCR's and they had emulsion tubes in the main well reducing fuel flow, so the larger PVCR was needed.
Now, the newer 3 Barrels came with metering Block # 5615 and had a .040" PVCR, and does not have emulsions tubes in the main well, and the primary side of the 3 Barrel is basicly the same as the primary side of the Holley 850 Double Pumper, so tuning is about the same. The PVCR's in the metering plate of the 850 DP are .070" and also do not have emulsion tubes in the main well.
So, to tune the 66-67 and newer 3 Barrels, you open the PVCR's on the #5616 metering plates from .040" to .070" and proceede to tune the 3 Barrel primary's the same as you would an 850 DP consiting of the fuel mixer screws, the transition circuit, primary jets and power valves. There are plenty of tutorials on line for tuning an 850 DP for referencing if you have questions. I'll add more later concerning the tuning of the 2ndarys, actually half of it s getting the primaries tuned.
