Won't Fire - Need Help!

Hey Guys,
Need diagnostic help and list of things to check...

Have a newly rebuilt 340 engine and can't get it to start. It's getting fuel and spark. Tries to start and backfires through the carb. It has 145-150 lbs. of compression in each cylinder. Used pressure gauge to ensure distributor is pointing #1 cylinder on the compression stroke. Used a timing light hooked up to the #1 plug wire and timed to 14 degrees BTDC. Has an MSD6A Multi-spark box and MSD Distributor with new cap and rotor...

Any thoughts on what could be wrong/off or what I should check?