I am messing around with my spring selections with my my Holley 750 vacuum secondaries. I have a mini day cruiser with a BBF , and a motor that runs around 4800 to 5000 rpm . Whats a good rpm to have them start opening ??

I know how i do it is put the lightest spring that works without bogging and dont worry about what rpm they kick in.
Just my .02 Tom

Pretty much it. Start light and work up 'til it doesn't bog when you flatfoot it is how I do it.

Don't forget to read your plugs as you're going along though. Could be chasing your tail if jetting, etc is way off. 

Ray