Then first we have to fix the 'idle circuit'. It's in quotes because the 'idle circuit' supplies also supplies all of the fuel at off-idle, low speed cruising, and a significant portion of the fuel mix at moderate cruising.
Without knowing more, the first thing I would suggest is checking the transfer slot openings on the primary side.
See where they are at now (length visible under the throttle plates) and then note the how many turns of the screw from closed to open the throttles enough to show .020", , 0.030", and .040". If you read the sidebar linked above they say .020 to .040 is the typical working range. I think with a QF its likely .040 is too much.
End of drill bit is next to the transfer slot.
The amount of slot exposure is about the same as the bit's diameter. A wire feeler gage can also be used.
View attachment 1715368666
The question about ignition timing, idle rpm, (and cam, and compression) is relevant because it works together.
If warmed up the engine wont' idle with .020 to .030 depending on the current timing, giving it a little more advance may be what's needed.
Alternatively, cracking open the secondaries a little more at idle may be an answer (or the idle-eze if so equipped)
Finally its possible a slightly larger Idle feed restriction(IFR) or smaller idle air bleed (IAB) is needed.
That's getting into much more advanced work, so that's why I left that to last.