Do a compression test first,all cylinder should be equal (+/- 5%)
Whilst its running pull a lead off(one at a time)and note the engine tone.The one that doesnt change the engine tone when you pull a lead off is the cylinder at fault.
Losing a cylinder could be down to faulty spark plug,faulty leads,rotor arm or dizzy.
If these are ok its probably not gettin fuel(or not enough,or bad spray).Could be an injector blocked or a metering unit fault.