Has it been sitting for a long time? Are you getting fuel to the carbs? Open the fuel drain on the bottom of the carb bowl to make sure. Have you checked to make sure you are getting spark at the plug? More info is needed to be able to help. Let us know what you have checked already.
Agreed - be detailed and wordy! Tell us history (had it 20 years, got it yesterday, etc.) and a progression of operations and problems leading up to the current symptoms. Then be VERY detailed about the symptoms and what, if anything, you have tried to resolve the problem to date.
Details, details, details; the devil is in the details!