It turns over very fast with decompressor …but would not start. I was thinking that perhaps decompressor is sized for a larger displacement motor and lack of any compression was the problem - but then it wouldn’t start kicking it with decompressor off. So no answer yet as lack of time to give it proper attention 
 

Well. I am still rebuilding my engine....   so let me know your progress.  Thanks.

I gather we're talking a 175 top end. Only way a decomp could work is to have one like a 360 bleeding off from above the exhaust port to soften the comp a bit. So talking our early yam AG175's & basically the same cylinder as an CT2 or 3, they had a drilling open all the time drilled probably 1/3 way up from port top to cylinder top. Drilled down to the exhaust port exit. Worked good for softening comp for easy starting, plus had a heavy flywheel which helped inertia. Sounded a bit fluffy at idle but didn't noticeably affect top end. If you're talking CT1 on your AT1E being piston port then same could be applied. Be a bit difficult to do though without good gear. I did that on my YZ465G for enduro riding & did the job ok & could block it off from the bottom if i wanted with a short grub screw--well that was the plan but never did block it before i sold it.

If you look closely at these pics on a random cylinder i found googling you can 'just' make out the hole.
My attempts at copy & paste the ebay link doesn't take so gave up & wrote it below.
ebay 113721060572

Wow RT325 I learned something new today 

Yamaha published a service bulletin on drilling that hole on a 175 to help prevent kick starter breakage. Enduronut posted once that there was actually a rare factory cylinder with the compression release hole drilled…

The chainsaw/Harley type should work fine…I believe they stay open until engine fires so if your bike doesn’t run that could be the issue?

Harley guys use them on high compression engines so starter can crank it over.