You had me worried about the Grose-Jet Valve
. Never seen or heard of a failure. Not even when I converted a left-over Grose-Jet to work on my 1925 Dodge Brothers using a Stromberg OD-1 carb..it never failed.
So after you successfully diagnose and repair the issue, if it has anything to do with the Grose-Jet, please don't tell me.