It’s been said a bunch of times above - you’ve got some sort of timing issue if it backfires. Make sure your timing marks are correct on the damper, use a positive stop on piston #1.

I’m lazy, and decided not to install an electric fuel pump. What I do when my dart sits and the gas in the avs evaporates - is I take a small amount of gas (about a 1/4 cup) and pour it into the fuel bowls through the bowl vents. Then it starts immediately !