I put the cdi on mine and mine ran with the other cdi. I did it that way because I knew mine ran and I could rule that out if mine still ran with the other cdi.

 

gotcha, i would try a compression check then, possibly a leak down to see if the valves aren't seating all the way.

when an engine sits for a long period of time, the open valves can form rust, and cause them not to seal up. this can show up in a compression test as low psi, squirt some oil in the cylinders to rule out the rings.

did you try spraying fuel, or starting fluid into the carbs?

 

starter fluid, and that would only catch and causes a backfire through the carbs. and it would take a few cranks after the squirt before it would backfire