I've got an hks racing bov - it has a vaccum source on the top port, and is open on the bottom port. Is the valve supposed to be open at idle? If I pull throttle cable just a little it shuts. Is this normal?

 

Think so.

 

If this is the old HKS racing bov there is a bolt on top to adjust the spring tension. Turning this bolt clockwise will increase the tension and require more vaccuum to open it the valve, so if you want to close the valve at idle to prevent unfiltered air from entering the engine, crank the bolt down...

 

Well, the f-max kit came with a smal k&n filter that fits right on to the blow-off valve, so I assume it goes on there for just that reason.