I would be looking at your throttle slide cutaway. Although only responsible totally for a small part of the throttle opening, it does have considerable influence. If you are running a 376/4, try a 376/3. The 3 or the 4 indicate the height of the cutaway in 1/16ths of an inch. Obviously, the lower the cutaway, the richer the mixture you will get.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.