I have a freshly built 400 that is having problems with the spark. I can put a timing light on #1 and 8. And it will flash like it should then randomly quit for a few seconds. I've already swapped wires around and it stays on 1 and 8. I've also put on a new cap and distributer but it's still randomly not firing. I can't think of any thing else it could be. Any help would be appreciated

 

Would bad plugs possibly cause it to randomly not spark when testing it with a timing light

 

Yes. Anything that stops the spark from going from the distributor to the ground will stop the timing light from blinking. Swap the plugs between cylinders and see if it follows the plugs.

 

Thanks I decided to try that before I saw your post and it fixed them. It finally runs like I thought it should have when I built it

 

Welcome to FTE! And congrats on the new engine and the fix. Well done!