Valve Float

#1
Earlier i was riding my go kart (yerf dog with heavily modified predator 212cc and hillard clutch) with the throttle fully opened and the chain fell off and the engine revved really high and sounded like it hit the rev limiter in a car. Is that valve float? I have 18lb springs. no I didn't get a chance to look at the rpm because I have a hard to see tach but it sounded high.
 
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