I have removed the rubber cover on the auto decompression and when kicking it over there is no movement what so ever. Tried adjusting the cable still no joy. I haven't removed the clutch cover yet but does anyone know how the cable connects internally? Is it a big job to sort out.
I have removed the front end and cleaned the carbon and oil, that bit looks all good.
It can't be working as the bike really kicks back.
Thanks
Also to test it can you remove the spark plug and operate the kick start lever with your hand to make it easier to see if there is any movement?

 Yes just remove the plug & have a play. Is the cable gunged up so its actualy stuck open rather than closed. Does it have compression you can stand on or just goes through soft. "76 400 looks like the shaft goes right in like a DT360A, so hope you can replace it without pulling the shaft out as it engages the spring right internaly but theoreticaly should have a catch on the spring drum to keep it preloaded. Bit of a crazy setup.
www.partzilla.com/catalog/yamaha/motorcy...tarter-250b-c-400b-c

Have you removed the mechanism from the head? I’ve just removed mine and the workings are quite simple. The plug (for want of a better term) moves really easily on mine. So, you should be able to establish whether it is a issue with either that, the cable, or the kickstart mech. If you disconnect the cable, does that move when you operate the kickstart. If you remove the valve from the head, you will be able to operate the kickstart easier to test for this.

It shouldn't really kick back or not enough to be a worry so hope the crank key is good that holds the flywheel. Hard to kick over though if no decompressor working. Just kick it against compression with the lever right up starting from the top once you've found compression.

Hi, my decompressor works but I still have high compression and if I dont get the kick right it kicks back on me, I think they are all like it. Im trying to learn the over top dead point to kick it. if its half hearted I get a sore ankle from the kick back.
I did find a weeping gas tap as when bike on side stand I used to get a puddle on the floor, when bike propped up straight no puddle, I think the fuel was filling the carb and then into the crank hence the high compression. Im currently painting the tank and aim to fit another gas tap, then see if I get the high compression or note with the new tap fitted assuming this does not leak

Make sure that the hole in the cylinder isn't blocked with carbon deposits.

In my experience a 360 or 400 that kicks back "regularly" has the timing advanced too much.  It doesn't take very much extra advance... just a couple degrees...  to turn one into an ankle breaker.  Compression release makes it slightly easier to kick over but it will still kick like a mule from the timing advance. 

With modern fuels they run great with ignition timing slightly retarded from original specs...  and Viola!  No more kick back. 

I've found a timing setting of 0.100" BTDC (2.54mm BTDC) works very well and is only slightly retarded from the "minimum" spec Yamaha gives of 2.75mm.  No perceivable decrease in performance and seems happier at higher revs.

P.S.  Two strokes are not the same as four strokes with regard to ignition timing advance...  they generally need less advance at high rpm, not more.  

My bike has had the complete 12v conversion.

mine also conversion and a fixed timing stator plate

You might take the time and check your timing with a light at cranking speed...  especially if it's one of the products that no longer uses a separate coil to trigger the timing.