Why do you need to idle the engine down for?The idle seams high and the screw to adjust is already off the stop . It seams like the rod has to be bent to lower the idle. I have to let idle for a bit before I shut it off or it backfires. The dealer supposedly could not find this issue
These are not car engines. Is yours water cooled? Full oil pressure lubed?
Low idle is around 1750rpm IF you dare to set it there. Do you have a tachometer to verify your rpm?