how can i fix my mini dirt bike?

we tavelled to australia from nz and packed our mini bike into its origanal box. it was running perfectly on xmas day. it was brand new and ran for about 2hrs .it was drained before putting away.it hasn't gone since. we checked the air filter, feul mix, carb and spark. it starts imediately after putting feul directly into the cylinder and it peters out in less than a second. sorry but we dont have make or model but it is a single cylinder 25-1 mix 2 strke motor