O.K. It's been a couple years since I drilled out Holley NH passageways. Today I began rebuilding a friend's NH and came across a minor problem while drilling the plugs to clean the passageways. In the attached photo that I shamelessly lifted from someone's past posting, the straw that is going into the long neck - inside of which is the jet - seemingly only goes through the hole into the open area inside. What does this hole do and why should it drilled out and then plugged? I can't see that it has any internal passageway for air or fuel to travel through. What is the purpose of this hole? Do I plug it flush with the internal threads for the threaded bowl drain plug?
I drilled out the brass plug and threaded the hole for a 10-24 plug, but am wondering what good this will do. A second NH that I disassembled has the open hole with NO plug. Now I'm confused.
The flow is opposite the direction of my arrows, it exits inside the carb throat through the 2 holes indicated by the dots. It is intersected by the diagonal passage which is intersected by the horizontal passage that opens up where the spray needle goes.
So it flows from the mixing chamber to the 2 small holes in the carburetor throat.
Thanks, Corey. That's just what I needed to understand the flow and straighten out my thinking on this subject. This photo with straws and directional arrows would have been a GREAT help if it had appeared in the MTFCA carburetor book. I'm sure it would have cleared up confusion in many a reader's mind.
Everything drilled, cleaned and plugged now. Thanks again!