Other times it will lock itself up completely and the only way I can start it up is with the compression handle fully engaged through the entire process. Worn quadrant? What do you think?
Your problem is the crankshaft nut isn't fully tightened...
You should tighten it until it comes up hard against the sleeve that carries the engine sprocket and then 'knock it up' tight with a hammer and aluminium drift or the correct spanner and a hammer if you have it....Ian