Ok I put my valve springs and what not all back together and now the engine won't start. It only backfires.

Durring this run of matenance I changed all the valve seals, took the opti off to make sure it was ok, and installed a new fuel pump. Now that it's all back together I can't get the car to start. It only cranks for a few seconds then backfires.

Is it possible my valves are adjusted that poorly? What all can I check before tearing the opti back off.... arg.... to make sure the dowel went in correctly (which i dinked around with to make for sure it went in right so I have a hard time believing its that)... Any ideas?

Thanks