Yes,you should see motor idle speed rpm
drop considerably or even stall when PMs
is almost closed or fully closed/lightly seated.
Possibly idle speed is set higher then it should be so throttle slide in carb
is higher then normal & throttle plate is also open further then it should be too.
Then in that case the motor would mostly be idling on the main
carb circut which is why PMS ajd didnt affect it that much vs with motor idling mostly or fully in idle /pilot
circut with lower idle speed adj dropping throttle plate futher back into idle/pilot circuts.
I have unb into that issue before from time to time.
Also,poss idle circut is clogged in a way PMS has not much affect but motor is still getting fuel to idle opn from idle/pilot circut,but i dont know if that can in fact happen that way.