how can i sort my piaggio zip 2/ 54 plate out ?

i have a piaggio zip air cooled 2 stroke 54 plate. i have just put a new 70 kit onto my bike an i was rideing an it bogged an thn cut out i thn realised my plug was abit loose so i titeghned it finger tight to get me hme.about 200 yards it did it again so i pushed it home and then the head of the bike was scorching hot i took the plug out and it was burnt. what could e causing this ?