I have had a few that have been sitting for 20 years or better. .first thing i do is check compression andfor spark..as stated if no spark i have found cdi box at fault...look for replacement on ebay or treats or doscycles..once you get spark and know you have compression drop the exaust because a lot of times it is clogged ,get a new spark plug ,put fresh mixed gas in the tank and see what you get ..i also use a little starting fluid most times..i didnt note but drop the exhaust before you chck compression because if it is clogged t might make you think it has no compression.