Gonna have to be alil more specific on the kart(pics/vid... no links to pic plz!), if youre gonna want us to know what you are talking bout...
As far as the motor... could be anything, w/out knowing more bout it. Could be carb needs re-cleaning... could be your coil/plug/leads... could be the on/off switch is 'off'. 7 outta 10 times its the carb that is an issue when it comes to small engines... next its the coil/plug/leads...after that its touch n go as to what could be causing no start(timing/something inside broke/etc).
Plz dont refer your questions, via mail... youll get a better answer by asking on a post like this...
Plz fill out your profile.