You were right! I removed the muffler and pulled it to see if it would start, but i didn't have the fuel tank attached, so it was only going to start with the small amount of fuel in the float chamber. It did start breafly, so i put it back together with the fuel tank attached leaving off the muffler. The engine would then fire a few times and die. Then eventually wouldn't fire much at all.

You;ve helped me make significant improvements i'd say. Thanks! Would you think that i now need to get new head and block gaskets, as i didn't replace them on monday when i took the head and block off the engine. Is it possible this is the cause of the engine not running properly now?

I've checked and there is still fuel and spark getting to the engine. There is also vapours coming out of the exhaust port when i pull the starter cord.

Cheers,
Trev