Ever had problems with getting your engine started, most of us have at one time or another. Here are a few things to check out.
Check for compression.
Turn the engine over by hand. As you turn the engine over it should become difficult as the piston moves up the bore the air inside becomes compressed. If this is the case then you do have compression and you should move on to the next check
Fuel Starvation
Firstly check that you have fuel in the tank, sound obvious but I have seen this!!.
If there is, check for blockage in the fuel line, remove the fuel tubing from the carb and blow down the vent pipe. As you pressurise the tank fuel should flow out of the disconnected line going to the carb. If it doesn't, then you have a blockage somewhere. Find the blockage and clear it.
Check to see if there is a blockage in the carb, remove the main needle valve. Blow down the vent pipe, as you pressurise the tank fuel should flow out of where the needle usually is. If it does, replace the needle and screw it all the way in, but don't overtighten it. Now turn the needle out 2 full turns. This may not be the ideal settings for your engine \ fuel set up, but if fuel starvation was the problem then this should cure it and will allow the engine to fire up.
Ignition
Check the plug. Remove the plug from and connect it up to your power supply or glo clip, if the plug glows then it's OK, if not fit a new plug. It's a good idea to replace your plug on a regular basis, I change mine after every gallon of fuel. Remember to check your new plug before you fit it.
Hope this helps