Has anyone done the Dirt Wheels mods on the z400?

They did a Motoworks slip on and instead of a rejet they used one of those Scary Fast inserts...

My only concern is that the z400 runs a little lean stock and IMO stretching that mixture even more might not be a wise idea in the long run....

I know DW said they liked the outcome but I wanted to see if anyone here had any real world experience with comparing the two options....

I am leaning towards the Motoworks pipe, it is a really nice piece of equipment.

 

Well, I have a Scary Fast insert & a White Bros. pipe & have it jetted the same as if I only had the pipe. 165 main, shimmed needle, & fuel screw out 3 turns. I had the pipe & re-jet before the insert, so therfore I never changed a thing after I got the insert. The inserts are WAY overpriced for a piece of aluminum, BUT work great!! The throttle response & low-mid power is greatly inmproved.