Jerry - I mildly disagree. If one is going to thread the carb body, it should be done for Carter jets, not Holley.
A few reasons:
(1) I have thousands of Holley jets in my inventory, and virtually all of them are too small for even a 216 Carter (remember the metering rod goes through the jet, so the jet diameter must be significantly larger). If you are going to have to make a fixture for your lathe (yes, I have one I made) to machine the orifice in the jet plumb, you may as well machine the press-in jets.
(2) Carter jets of the correct range of sizes are also readily available
(3) The profile of the Carter jets is designed for the metering rod, the Holley jet is not.
As few as 10 years ago, every FLAPS in the USA stocked Holley parts (obviously, because every Holley in the USA needed parts
); but this Holley advantage is no longer true in many areas. None of my FLAPS even stock mounting gaskets today. Just as easy to order Carter jets as Holley jets.
Incidentally, many (I am not going to check them all) of the Carter YF's do have the spring Jerry described that Rochester used on the Q-Jet.
Jon
