You can often borrow a compression gauge from your local autoparts house.
Basically you pay and then they issue a credit.
If you have one cylinder not getting fuel with a dry plug, but has spark a compression test might show something.
I think the 4 cylinders have two carbs so one carb feeds two cylinders ao one not getting fuel from a carb is unlikely.
Reed valve or no compression since the down stroke is what moves the mixture from the crankcase to the cylinder.
Those reed valves keep it from going back into the carb.
So when the piston goes up it sucks air and fuel from the carb into the part of the crankcase under that piston.
When the piston comes down the reed valve close and the mixture is forced from below through the transfer ports to the top of the cylinder and are compressed and then the spark fires it and the cycle continues.
https://www.youtube.com/watch?v=xNLE8G3pC0k
A compression check will check the reed valves and the rings etc.
If you pull all of the plugs and spin the motor you can see and hear the air blown out of the plug holes, but be careful that air has fuel and if the plugs are not shorted out the spark could make a nice big fire.
By the way spinning the motor over with no load on the spark coil will let the voltage go very high and might breakdown the coils insulation.
