only three things can stop it.....well two. your getting air. Spark and fuel.

Pull a spark plug and leave it plugged in, if it is orange spark it could be your coil. also if it doesnt fire is a good indication too.

cap and rotor or timing is off. Get it to TDC by clicking the motor over until you see the timing mark lay tdc. then pull the cap off and check if it is alligned to #1 fire.

check the filter. Should be inside carb from the line on pass side.