What did I do wrong?

[idaho66stepside]

Well did the engine swap last weekend and got the 350 bolted in. The HEI dist. is hooked up to a hot wire and the I think the mechanic that put the engine together installed the hei at TDC, the engine fires but doesn't idle. It cranks up then backfires or shoots a geyser of gas out the carb (edelbrock 600cfm). I'm thinking it's timing but that is like japanese to me. any suggestions that someone with limited engine knowledge could handle