I have the same idle issue with the IO-360B1B on my -7A when the weather is warm and the engine is hot but was never too concerned as the stumble disappears as soon as the throttle is opened. After reading this thread, I got curious and emailed AFP to see if they thought changing the spring in the fuel divider on my FM-200 FI system would help. Kyle at AFP responded as follows:
"We do not make a spring that will move our flow divider opening pressure to 4 psi. We do sell that Precision part number spring, but it will not increase the opening pressure of our flow divider for its spring rate is already the same as ours. The diaphragms areas are different, so a 4psi spring to them is a 2 psi in our F/D. They do that to try to increase the back pressure to raise the vapor point. They do not make smaller nozzles so that is their only way to try to help the situation of vapor. We change to a smaller restrictor size in the nozzle so it will raise the vapor point from the nozzle back to the fuel control vs the flow divider back to the fuel control. Sometimes that can help as well as looking at the install to see if it can be cleaned up(shorter hose routing, no pressure cowls, no gascolators, transducers before the pumps or on the firewall etc). You can drop the restrictors to .024's in all the nozzles to see if it helps enough."
Restrictors
https://airflowperformance.com/index.php/product/special-restrictors/
As a side note, Kyle also stated that flow dividers and fuel controllers should be overhauled every 8 and 12 years respectively. I didnt know this and mine are greatly overdue, although still seem to be functioning just fine. Same deal for Bendix/Precision systems.
Overhaul period
https://airflowperformance.com/wp-content/uploads/2016/05/Overhaul-Period.pdf
Overhaul forms
https://airflowperformance.com/wp-c...r-form-for-FM-Overhauls-Rev-November-2019.pdf
Erich