Cam chain tensioner - again

I discovered while adjusting the valves on my kz650D1 that the cam chain tensioner was bad. I found an identical replacement at a reasonable price that appears to work as it should (the bolt can be removed, the tensioner's rod moves freely in and out of the bore it's in) at the local boneyard. I've re-shimmed under the buckets, re-installed the camshafts as per my Clymer's and installed the tensioner. It doesn't appear to be doing much of anything; when I rotate the engine via the 17mm nut on the ignition advancer, the cams turn, the chain tightens and then .. slap .. all the tension leaves the chain and the engine lurches forward. I'm pretty sure that it's the tensioner that's not doing its job although I will be re-re-re-checking the camshaft installation to make sure I did that right. Any advice on how to install a stock replacement tensioner? Thanks.

have you got access to a shop manual?

I've got a Clymer's but it's not been helpful with this or even some other items (like removing the tach pinion). I'm hoping for some "real world" advice.

This is a really dumb question I know, but are sure you are not turning the engine backwards??

The book says to turn the nut clockwise and that's what I've been doing.

You are tightening the lock bolt on the tensioner before attempting to turn the engine over I hope? These tensioners don't cause any trouble generally, but if you turn the engine over with the bolt loose there will be problems.
Another tip about the tach pinion. Leave it be, no need to remove it unless it's leaking.