is it popping through the intake, if so, the dist could be 180 out. if not, try advancing the timing a bit at a time until it cranks really hard, if it still dont start, you may not have adequate power coming out of your ignition module if its an HEI. i had that problem about 6 months ago. it would show it had good spark, but it just wouldnt kick ya know. i ended up replacing the module and everything inside the distributor connection wise. good luck.