RE: Saito 100 No muffler preasure
The engine will run without muffler pressure.
It sounds like you either have a leak in the intake tract or there is a valve timing issue.
Check at the carb base or where the manifold enters the cylinder head for leaks. This assumes that the engine is timed properly and that the valves are operating when they are supposed to operate.
A timing error in reassembly will also cause no suction at the carb to exist. No suction, no fuel. Go over your timing again.
Ed Cregger