The plug wire should fit very snug, dont fly unless its secure!. Is it a rubber bootie or is it a bosch type end? Is your ignition battery charged fully? Do you have the braided ground wire clamped to the base of the spark plug or to the head? Do you have the correct spark plug intalled? Can you see gas in the fuel line? I dont have experience with FPE engines but when trying to start it, usually you have the throttle at idle. I know on the Brison engines much throttle and it will backfire. For safety I would not like to be flippin props above an idle.

Good luck,

Jerry