Stu

"It ran before I took it apart, and the only real change is to a pod type air filter."

So what bits did you take apart?

IMHO a pod filter probably would not make a lot of difference to it starting, but would probably affect the running under throttle.

Assuming timing is correct, I wonder if by coincidence the plug has decided to pack in - it has been known, perhaps it is not sparking under compression?