You mention it has a new plug and plenty of compression BUT not that it actually has spark.
When I start to run out of ideas I always go back to basics.
Check that you actually HAVE spark and that when the throttle is moved to stop that it DON'T have spark. That will show you whether the kill switch is working properly. Then take the starter off and check the o ring. I usually just change them anyway as they are very cheap. After that change the inlet manifold O rings. This will all make sure there are no air leaks.
Are you getting fuel to the spark plug? Remove the plug and touch/sniff it. If it is dry and no fuel smell you are not getting fuel through and there is a problem in the carby. IF it smells like fuel and is damp then the carby is fine. If it's soaking wet then its a problem in the carby.
Try putting a teaspoon of fuel in the spark plug hole and see if it fires.
Work your way through the problems systematically and you will get it going. You may aswell change the primer O ring and cap while you're there.
If all else fails check that you have the correct main jet. Someone may have changed it and mixed the jets up between LM and G4 carbys.
Take it slow and work systematically and you'll get it going.
One more thing, You say it has great compression - how are you measuring this? Is the decomp valve working?
Pete.
