Depending on the design, it may not have a removeable restrictor. On some, it is obvious right on the inlet; on others, you have to disassemble the whole thing. On others, it is just designed for the specified flow - to change that, you'd have to drill things out to make the passage ways bigger. If you can't find it on the one you have, see if you can look at some at a store that aren't in a blister pack (well, on some you can see the thing). Basically, if it is in the path of the inlet, and has holes in it blocking some of the path, it is essentially a restrictor. Modifying it by drilling things out is as you should realize, cannot be put back to the way it was!