Idel problem!

[TRX-330]

Ok so my friend and I are working on his 400 in school. He just rebuilt it, new rings, stage one hot cam, big gun rev box, timing chain and tensioner. Well he had got a Jet kit also because he was gonna jet it for the cam and the pipe he had on it. He did a new needle, and messed with the main jet. Thing is it wont idle, I told him he needs to get low speed jets because of the cam. Teacher said he needs a bigger carb. all together which I don't think is true. So my question is will all that stuff what do you think it could be? It runs but wont idle on its own you need to give it gas, but it pops real bad and backfires. At high rpm it seems to run decent but could be better. Oh and when we turn the fuel off with it running with will idle on its own once it gets so much gas out of the carb. its like its getting too much fuel.
Thanks guys

[arsenal35]

change the pilot jet I think stock is 38 bump it up to a 42 and that thing will puur like a kitten if its backfiring it's running lean the pilot jet controls gas flow up to like 1/4 throttle. but 42 pilot jet. That will solve all your probs. Oh yeah and th epilot jet cost 4 to 5 dollars

[TRX-330]

Ya thats what I was telling him, he needed to change that one too! haha thanks for the help man.