Well I'm sure you have already done this, but it never hurts to list out the obvious...

1. Pull plug #1, stick your finger up to the port and turn over the engine until it sucks vacumm. Then you will be sure you are set at firing #1.

2. Double check your spark plug wires are not crossed.

3. Pull the valve covers and recheck your lash on the valves. You certainly could have them too tight or even broke a spring. Once you have set the valves, turn the engine over without the coil hooked up and inspect the valves to make sure they are all opening and closing.

Since you have tried the timing already, I bet DHOTROD & Grump are right about the valves.

Good luck and keep your cool...you will probably laugh about this later. You'll figure it out.