Buy a Gary Denton stabilizer. The PEP's work, but they are weak compared to the Denton, especially since the price went up on them. I had a PEP on my 300EX (that I paid $99 for, now they are $129) and it was sufficient, but the non-rebuildable Denton is much more serious. More adjustments, and just better built. The 3 adjustments on the PEP is a real joke. If you call Denton Racing directly, they will sell it to you for $125. The more expensive rebuildable Denton, just doesn't fit on a Z400. They claim it fits, but a buddy ended up sending it back for the less expensive, non-rebuildable model.
-QuadZ
8O