Please Help! Started truck for the first time and fire came out of the headers.

[Hazieview]

Hey guys I built my first engine ever and when I went to start it fire flew from the headers and it would not start.

The gears on the timing chain were lined up on the dots, distributor was put in at top dead center, carb was never adjusted from factory (edelbrock 650).

Any recommendations? Should I advance or retard my timing by turning the distributor? Cut my carb back on fuel?

Please help.
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