FWIW
I rebuilt carburetors for a number of years and rebuilt about 100 carburetors. I used PPG DP90LF (Black) epoxy primer.
http://www.custom-aerosol.com/pdf/PP...duct-sheet.pdf
I removed all brass plugs, and made my own plugs that had an Interference fit. Removing the plugs provided a greater degree of assurance that the passages were clear.
I painted all interior passages using a pipe cleaner. The interior and exterior were painted using an airbrush. The final exterior coat was painted dry coat with the air brush to achieve the correct luster for fine point.
Do not be afraid of removing the brass plugs! Start with a small numbered drill bit and increase the drill bit size incrementally until all that is left of the plug is a thin wall brass tube which can be easily removed. If you try to go fast and do not incrementally increase the drill bit size you can bite into the cast iron body and break a drill bit or drill the hole too large of a diameter than you want for an interference fit. Obtain some small diameter brass rod, measure the OD of the brass rod and then drill out the hole so you have an Interference fit. Chamfer one end of the plug and install with a touch of shellac for installation.
