I'm getting some fierce kick backs from the kick starter so I removed the cover from the automatic decompression unit and kicked it over a few times - it doesn't seem to be moving at all.
I will strip and clean but is there a 'figure' or explanation anywhere on the adjustment?

Thanks

Ideally shouldn't kick back unless the crank key is compromised, or pulser firing off early. But with the decomp i'd think would have a midway adjuster on the cable--without looking. In the first part of the kick movement you should have the decomp depressing unless the cable is broken or way slack on adjustment, or something is amiss in the kick mechanism. All a guess of course. Can you depress the decomp valve by hand. Is it blocked with carbon, think its head off to remove it to swing a spanner. Check the flywheel crank key--must be tight.

when you move the kickstart by hand the cable should if I remember go slack and allow the de comp valve to retract a couple of mm to let the gasses escape into the exhaust. when the kick lever is in its home position the cable tightens and closes the valve off.
thats how mine is working, but I still have high compression and I get kick backs as well

I've always found timing is much much more likely to cause kickback than the compression release not working. 

Slipped flywheel with sheared or partially sheared key in not uncommon or on the later models those darn CDI's start to go rogue.

Moving the kick lever pulls on the inner cable at the valve moving a little arm to push the valve in & let the gas past. So reading the first post it's no moving at all i see. Only adjustment is on the cable so then the problems start finding out why not moving
www.yamahapartspro.com/oemparts/a/yam/50.../decompression-valve
Page 28 shows a drawing of the mechanism in the clutch cover but not much else. Really need to go in there if the cable isn't broken or rusted & stuck in the open position in which case the compression would be low.
yamaha-enduros.com/index.php/service-man...ctory-service-manual

I upgraded my ignition to a rexs speedshop electronic unit. when I got the bike as I assumed my starting issue and over run issue when hot was the cause of the stock ignition system. I fitted a new woodruff key at the time and the coil backplate is fixed timing. I still had the same issues afterwards, so the stock kit I removed was good.
Im slowly getting the hang at starting but I still get kick backs, however today in rainy freezing uk I started of first kick so was well chuffed

The only way to know it's not firing too early is to mark the flywheel and test timing and crank over speed with a good timing light.  360's and 400's are very sensitive.  A couple of degrees more timing will make it kick like a mule.

It's very possible to exchange an ignition with slightly advanced timing with another one with slightly advanced timing.