When taming an achatina try to get them in a safe place. Once that's done you should shoot it in the head with tranq darts/arrows as the shell does less torpor. Then feed it sweet vegetable cakes and BOOM your very own achatina!
Starve taming doesn't work too well for 2 reasons
1. It's food bar may be small, so it may start losing health before it even gets close to tame time.
2. The cool down gap for eating cake, means that you need to factor in the eating time.
Hope this helps