Can the spark show on the outside and not on the in?

Help please ..
Zip came to halt and the fan had disentegrated on the variator. Maybe coincidental. Anyhow after cleaning that out it won't start. I have a spark/changed the plug. I have changed the fuel as it was after a fill up. I have been through the air filter box, carb, reeds and even put a new s/h barrel and new rings on it. Exhaust I can blow through.
I am wondering if a spark outside can breakdown inside. Anybody know? TIA