hmm.. something don't add up here.
a 9n is a front mount setup. it's only 'coil wire' is the primary wire from the resistor to the top of the coil primary. and 6v ain't gonna jump no 1/2"
only places on tht frontmount you can get a spark jump is from one of the 4 wires coming from the cap.
in general, increasing the spark gap and making it fire means you have a fouled plug.
now.. is this REALLY a 9n with a front mount? or does it have a round coil conversion? or is it a round coil later engine on a 9n and you just don't know what type of machine you have?
in any even. if you are pulling 2ndary wires to get a spark gap / jump and it fires. look for a fouled plug.
post back some details.
questions like this devoid of most of the usefull clues needed to solve the issue always intrigue me. :)