ok. 1)plug glows orange redish down to about half a coil from bottom, no breaks and deformation
2) fuel is drawn into carb straight away
3) head, backplate, carb secured
4) engine mounted fine
5) turns over easily with the head removed. with the head on the cylinder should retains compression seal when the piston is brought up to TDC.

i think the plug could be the problem any other ideas



edit for typo