just to add.
slowly increase the mixture, not fast not extremely slow to half way then then you will hear it clear.
start the right engine 1st
why
so you can hear it.
then the left
why
cause you can hear it cleaner because its closer to you.
you will notice engineers always start r/h then l/h
so today I started two c400 serries engines that 4engines in total.
the 1st aircraft 10 c oat normal cold start 750 rpm both engines
2nd aircraft approx. 24c 740 both engines on start
happy days