If it won't fire with fuel in the cylinder, you have insufficient spark or compression, or the spark is happening at the wrong time. You might learn a bit more by removing the muffler and checking the exhaust port is clear (leave the muffler off), replacing the decompressor with a spark plug, and trying the fuel-in-the-plughole trick again. You should be able to feel the compression - both crankcase and cylinder compressions - quite strongly then. If you can, and it doesn't fire, there is something subtly wrong with your ignition.