Wildwill,
I haven't bought or used one. Just do a google search on the phone number for Holtzman and there will be some mag write ups and photos. Pretty interesting. Then give him a call, like XC800 said.

 

This Holtzman gizmo looks pretty good. I seen it on XC800 sled fairly basic hook up, when I was looking for an adjustable jetting add on I was hopping for a jet that operates on the bottom of float bowl. The only one I could find at the time was Dial - a - jet as it was the only one that would operate on a down draft carb. I have seen these on some race bikes where alll you have to do is turn a rod on the bottom of the carb which increases or decreases jet size so you can be in the between sizes of jet. For general running around where you set it once and run to what ever elevation without having to adjust the jet the Hotlman works excellent. For my application I use it for delivering race fuel to the engine at controlled pressures the Holtman is not designed for that operation. If I were to install another adjustable jetting system I would certainly look at the Holtzman. Although EFI will eliminate all jetting questions in the future this is the way I am going.