What do these passages do. Is there a diagram that shows them and their function? What are they plugged? Can they be cleaned without unplugging them?
Do a search and there is a picture on the forum showing all the passages with wire running through them.
I saw it. Can you clean them without removing the plugs? What is there real function?
Here is the "Wire Picture".
No. You can't clean them without removing the plugs. Stan Howe, whose business is restoring carbs, suggests using a piece of brass-wound guitar string. That's rough and hard enough to dislodge dirt and soft enough not to damage the cast iron. You can replug the holes with brass welding rod, or tap them and put in 8-32 Allen set screws that can be removed for cleaning. Be sure the air vent under the tag is clear.
There is an excellent technical description of the idle circuit and a cutaway drawing of the NH on pg 282 of the Ford Service Bulletin essentials. The MTFCA Carburetor book underemphasizes the function and need to clear these idle passages when doing a rebuild. The vent passage is more easily accessed. It was initially unclear to me from Bob's pic exactly how the 3 idle circuit passages connect, after cleaning a couple of NH's, it seems trivial.
Drill the plugs carefully! I drilled and tapped the brass plugs with 4-40, and pulled them out with a stainless steel machine screw. Made short 1/8"diameter plugs from brass rod, tinned with solder and drove these into the holes. Note, the plugged passage into the 'well' above the spray needle seat is parallel with the bowl flange (perpendicular to the spray needle)and the service bulletin indicates the diameter of this passage (3/32")is responsible for metering gasoline during idle. Don't drill that passage, or any idle passages, use brass wound string or aluminum filler rod to clean out debris. respectfully, jb