Thanks guys, I took off the cylinder head and cylinder. There was a bit of coke build up in the exhaust port, I've cleaned that off, high pressure hosed the parts, cleaned with a cloth then put the engine back together.

There seems to be compression twice on a revolution of the engine, so I think the compression in crank case and cylinder is fine.

I think its looking like an ignition problem, i've regapped the E-Core, the spark is there and is blue. Like you said perhaps it is firing at the wrong time. How do I adjust this? Is it something to do with the electronic ignition module?

I really appreciate your help so far. it's great to be learning.