Did you check for spark on each new plug wire?
Then make sure your carbs have fuel, if you have an electric fuel pump, turn on key, then open the plug on the float bowls to check for fuel flow. Your engine sounds timed so there is no issue there
The orange air box is meant to be removed to allow for adjustments to the carbs...so they should run without them, if not, then adjust them to rule out any other issues.