Okay, so i recently installed an 80cc engine onto a bike of mine, and it won't start. When i release the clutch, i can hear the pistons moving up and down, but it never fires. I have removed the spark plug and tested the spark outside the cylinder. There is a good spark. I have also disassembled and cleaned the carburetor. The bottom of the spark plug smells of gas, so i know it's getting fuel. Could it be that the spark plug is not firing under the compression? If so, what should i do? any suggestions would be fantastic...I'm starting to become quite frustrated.

Thank You so much!!!!