Hi mate,
If you've had the starter off I strongly recommend replacing the o ring. There are 2 o rings on the manifold too. A small one and a slightly larger one. These ones wear out less frequently BUT it's worth checking. Also the spring washer on the manifold could be worn out. May be worth checking that out later if nothing else works.
Biggest question though is do you have spark? If not try disconnecting the kill wires and see what happens.
If the rubber boot on the kill pin is worn it MUST be replaced. When the rubber boot is work either kill switch will not work and you will ALWAYS have spark OR you will NEVER have spark.
Test out your decomp valve (attach clean fuel line and suck on it. If it closes then it's OK). After that think about the head gasket. If that doesn't fix it keep it for parts and get another one. These engines are fantastic but a dime a dozen so don't waste too much time and money getting one to work.
90% of the time I find it's either a leaky primer cap O ring, leaky starter o ring or incorrectly fitted/damaged kill wires.
Good luck.
Pete.
