If your engine isnt starting then work your way through this guide to identify and fix the problem.

*** Firstly start off by checking that the fuel petcock is on and you have fuel. Check the wires to the CDI. Make sure that they are connected. The cheap connectors can come loose.
Wiring goes:
White (if there is one) don’t use. Cut and cap/tape off
Kill switch – 1 to blues, 1 to blacks. Doesn’t matter which to which.
Also – disconnect the kill switch wires while testing out.  If the kill switch is bad the engine will not start.
1. Remove spark plug.  Make sure it’s in the cap nice & tight.
2. Check for spark with lead on plug and ground the spark plug on cylinder head fin or head nut (bare metal)
Lift the rear wheel, and give it one good hard pedal down as if you are
kick-starting a bike. If plug sparks at the tip, re-install the spark plug.
2a. If no spark, check Plug cap.
Check for spark again.
That’s the electrical done from start of lead to end of plug tip.
*** If Spark, then go to Fuel. ***
2b. If No Spark, go to Magneto and CDI.
But don’t just replace the Magneto and CDI unless you do all the above as well.  That way you have a clean sweep out of sight out of kind type of thing of the electrics.
3. Fuel.
Remove carburetor, AFTER Spark is all clear as explained above.
Remove fuel bowl, see if it was full or any fuel was in there.
If not, check fuel line and needle/seat where the fuel line plugs in.
There may be some grit.
If it had fuel in fuel bowl, re-fit carb.
Fuel is OK up to fuel bowl end.
4. Clutch adjustment, just go through the motions at the cable end. There should be no slack.
These instructions are fool proof. If none of these steps work, try it from the top again – you may have missed a step.