ok I have a 2 stroke 250 trailblazer that I got off market place have been replacing a lot of parts on it as it was a farm rig was riding it a couple weeks ago shut it off to fill it up with gas went to start it back up it cranked and then huge back fire and kicked the pipe of the slip joint and split the boot between the carb and head replaced the boot popped the exhaust back on and now when it goes to start it revs out super high like I have the throttle full open have pulled the carb off and cleaned it an made sure the slide is free my next thought it that it may have blow out the base gasket or crank seal just need some input if my thoughts are correct or there's something else I should check for

 

i would say it's sucking air somewhere for sure causing it to run lean and rev as you described .