I think i know what it means, but can someone tell me more?
Paul - It means that the passageways have been cleaned and re-sealed.
Here's a recent thread on the subject with some great information and suggestions:
Drilling a swayback NH can also be a cheap way to get a staight through..
Bob Cascisa in Poulsbo, WA posted some test reports in 2009:
OK, I thought it had to do with removing casting material from where the needle valve is mounted to give it a more straight through flow.