72 ford F250 won't start help

[69bronco]

hey i got a 72 f250 that wont start and i need some help, im 14 years old. the truck was running then it just stoped running and it won't start. the engine is geting gas,spark,and it has good compression. It has new points and the timing was right. but it wont fire. but went i was working on it tonight i found out that the carb is blowing air out insted of pulling air in. so what would make that happen?? , did the cam or timeing chain break or something? thanks