J engine fizzling spark plugs

[boof57]

Hi I have two J karts in juniors, one is perfect no issues at all the other one I have to change plugs twice at least per meeting as they just stop working. I take them out put a new one in and off it goes. I tried cleaning the other plug put it back in and no go. Its as if the plugs gets zapped and are useless. In two meetings I have gone through six plugs. I have tried different fuels and different mixtures. I am using B8es plugs in both karts as the the kids are only starting out.
Can anyone help that may have had the same issues.
regards

darren