OK, you have a good spark and your plug leads and fuel lines are the right way round,you didn't say that you had verified fuel was actually getting to the carburetor but if it's leaking out of the crankcase join we must assume that it is,you previously said you had 90psi hand pulling on both cylinders,which is good. So,if these three things are correct theoretically the motor should work, I don't recall seeing mention of the idle settings,correction,yes i do,anyway low speed (upper)full in then 1 1/2 turns out, high speed (lower) full in then 1/2 turn out.Pay particular attention to the packing on the needles,I put at least two washers on as a rule.
Make sure you open the twist grip as far as you can when starting,the slow fast shift thingies on the grip don't mean much,just make sure you are in neutral.
If it still won't go the problem must be with one of the three above,if it was not for you saying fuel is leaking ay the join I would go for a stuck float needle or some thing equally silly but good luck and let us know how you get on