Compression, spark, heat...what's missing?

the reason you can remove that one and it dosent kill the engine is that its not working, and when you remove one of the other 3 it dies it is now on two cyland will die.

you need to run a good compression check on all the cyls, check the timing with a light, by the way you can use the timing light to check for fire also,check the valve clearances, changes the plugs with new ones, then look at the carbs

Due to the wasted spark set up, if you remove one spark plug wire, and keep it away from any metal so it's not shorting to ground, you will lose "two" cylinders.
If you remove the plug wire for #1 cylinder, you kill #4 cylinder as well, if you then remove the plug wire for #2 cylinder, then you also kill #3, and that leaves you with zero cylinders left running. And your bike is not going to run on zero cylinders

#1 and #4 share the same coil, and #2 and #3 share the same coil.

Clear as mud?