how can i get my piaggio nrg sport 04 plate to work ?

i brought a second hand piaggio nrg sport series 50cc moped. pushed it home and tryed to get it to start.. it has no keys with it so it has to be started of the kick start. it has no airfilter in the airbox. there is a good spark from the plug but i have noticed that there is a black pipe coming from just below the carb, when i kick it up the compresion comes out of it. i have managed to get it started a few times but it just dies :( doesnt even rev.... i also have to block the pipe coming from the carb with my finger to stop the compresion coming out to get it started. very anoyed with it please help