In my experience, the cause of kickback is almost always timing too advanced and not "technique"... 

Exceptions might be if someone has a very weak push through or thrashes away at the starter lever as fast as they can like a madman.  Bring it up on compression, reset lever to top of stroke, and give a good push through.  If it still kicks back I agree it's likely timing. 

Could be pulsar or could be someone has messed with it at some point. 

So its Back to the Future with points then, Let's go!! One wire & simple. I'm running a champion N59G [just coz it happened to be in the head]. Also was running those funny surface discharge NGK plugs called BUE something which i thought look super cold [but are they?] anyone know.

Hi Guys
thanks for the tips I will try them. For info it is a1975 bike and it is fitted with a rex speed shop ignition unit. before this was fitted it did the same. the timing is fixed on the rex kit

Yeah I’m too anal that way as far as changing the Yamaha design…all my bikes run what Yamaha brung…pulsar coil and all. My 76 DT400C has no kick back after rebuild. Decompression hole in cylinder probably plugged on yours unless it was cleaned out recently.

can this be cleaned out while cylinder on the bike?

It is a very tricky little task as you have to take a device in from both directions to get it. I use several different picks. Going in from the exhaust port your tool can be as long as the width of the exhaust port because the hole is perpendicular to the exhaust. Same thing in the decomp valve opening in the cylinder so you can see pretty limited on size because of small diameter opening. I’m always amazed how blocked that little hole is and equally amazed at how big it opens up to. I’ve always opened it up as best I can and then sand blasted to get it all cleaned out. Obviously done off the bike during rebuild.

I will remove the de compressor unit and take a look/poke

Remove the rubber cap on the decompression valve and check and see when you kick it over if the valve is being activated by the motion of the kick starter.  If it is actually pushing the valve inward you should be able to hear air hissing out the valve..  You can remove the valve  assembly completely and then when you kick it over it will loose all compression out the hole.  My experience has been even though the decompressor isn't working that if the pulser is working correctly the bike will not kick back.  It will be a hard kick over because of no decompression..  I have no experience with the REX'S ignition product
doug