mercury bobcat need help carbs

help i live in california and law requires 77and up to be smoged, my problem is they said my timin=ming was off. so while trying to set timing i have run in to a problem with seting the carburators curb idle it says set timing with curb idle at 750rpms but this scewie carb ajustments i cant get it below 1000rpm befor it dies any help would be apriciated