If a squirt of Starter Fluid doesn't result in some VvrrroooOOom.. , the spark plug is not sparking (or maybe there is no engine compression).
Pull the plug and ground it's base to the engine block's fins with a spring clamp. Attach the boot, crank the engine and you should see the plug tip sparking.
As far as inadequate compression, that Starter Fluid is pure ether (with a bit of lube) and should even burn in the open air without any compression at all.. So, im gonna guess you aren't getting spark.