engine will spin over but won't crank.has new carb,fuel line ,filter and plug?

 

No different than a car, try jumping the starter with 12 volts, if it kicks in , then it's probably the ignition switch. Check the connection at the starter. Also check voltage at battery, ATV batteries are famous for crapping out.

 

Find out if you have a spark by removing the plug, refitting the lead and laying it on the head. If you don't have a spark, unplug the voltage regulator. Don't know why but on the 450 only, a faulty regulator often cuts the spark.