PIERRE PAGE, you need 4 things for the engine to work, Spark, Air, Fuel and compression. Make sure that you have spark, check the plugs, your ignition coil, and make sure your ignition air cap is set correctly. Make sure your carburetor float is not stuck, that your gasoline is fresh and that the float valve operates properly. Check your fuel filter, make sure it is not clogged, make sure your fuel lines are properly routed and check the jets in your carburetor, for dirt and maladjustments. Check your valves to make sure they are working correctly, set the valve lash as needed. Let us know what you find with further trouble shooting.