My VPI MK3 skips if I walk near it.Should this be?

My HW19 III used to do this, too. I am not aware of any spring adjustment. To stop it, I braced the support shelf against the walls behind and beside it. (It was in a corner.) I also inserted folded paper shims between the plinth and the wooden base, to change the resonance of the whole system. Good luck.

Assuming this is a new location for your turntable, the problem is most likely a "bouncy" floor, not an issue with the turntable or arm. As suggested by Jameswei, you might want to look at ways to make the support platform (rack, shelf, whatever) more stable and isolated from footfalls.
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VPI has reversed course on the springs and before dicontinuing the series they went back to sorbathane pucks on the MK III and IV.

They actually sell the older design pucks to retrofit the tables that were sold with springs. Who knows they may give 'em to you. (I doubt it)

I have a MK III that has the pucks and there is no bounce when used upstairs on a pretty springy floor. My previous suspended Thorens bounced if I even thought of walking anywhere near the TT and the VPI resides in the same exact location.

So just change out those springs for the sorbathane pucks.

Good Luck
Paul Green

Paul's comment is on the money. I have had a VPI HW-19 Mk4 for many years, and my older home has rather "flexible" wooden floors. Like you, the tonearm on my VPI TT bounced whenever there were footfalls near its' location (it even bounced if our overweight cat jumped down from the couch to the floor). I tried a lot of different approaches to solving the problem, and none were totally effective.Then, about 2 months ago, I replaced the TT's spring suspension with the Sorbothane pucks from VPI, and I no longer have a problem with tonearm "bounce". (An added, unexpected "plus" is that bass frequencies seem tighter.)

The pucks (and the Scout / Scoutmaster cone feet) can be purchased from Elusive Disk. Here's the link:
http://www.elusivedisc.com/prodinfo.asp?number=HW-2039

Installation of the pucks requires some minor changes to the turntable. Rather than go into all the details here, please drop me a personal E-mail and I'll tell you what to do.

One other comment: if you decide to buy the Scout-type cone feet, note that it is less expensive to buy them separately from the pucks, rather than buying the upgrade package which includes both items.