King cat won't engage till 4300rpm after overheat

So I need some help not to sure what it could be so I just rebuilt my engine one my king cat 900 and everything was good engaging at the regular 3200 rpm and I didn't let the air lock out completely did 2 slow laps around the house and almost ever heated so I lifted the front end off the ground pretty high and owned the cap squeezed the hoses while running got the bubble out refilled all while slightly reving it up a little now it's circulating and not over heating but won't engage till about 42-4500 rpm and like no botom end just try cat walk and idea thx in advance

King cat won't engage till 4300rpm after overheat