The stock jets on a Holley 600 4bbl with vacuum secondaries are #66 primaries and #76 for the secondaries for a 4150 carb or the equivelent for the metering plate on a 4160 carb.Holley jets larger than mid 60 numbers are not a drill size,but a stock number.
The stock Holley 600 primary jets are just a tad rich for a mildly tuned small block V-8's,going down a few sizes is ok.But if you change jets more than 6 or 8 sizes the carb is incorrect for the application.And reducing or increasing jets sized affects the high load mixture provided by the power valve.
