Good afternoon, I have a 2011 beta evo 250 2t. Had it for a couple of years now. Having s issue where when I rev it, it can take ages to come back down. I have tried messing with mixture screw and doesnt seem to make any difference if 2 out or 3/4 out. I have had the card apart and clean all indivicdual components with carb clean. Again no difference. I have tried to spray brake clean at intake system to see if it revs it doesnt change. Am I right in thinking this could be the crank seal? Or am i barking up the wrong tree? Also its does idle fine. TIA

Could the cable be the colprit

New throttle put on, cable oiled and free as a daisy 

What carb is on the bike? Should be a pwk, but old enough it could be anything.

It is a pwk 28

 The jet tower gasket can leak and cause all kinds of poor behavior. That`s the piece inside the carb with torx security screws. The original gasket can shrink. The mating surfaces are not very plumb. Some people have good luck filing the surfaces flush. Sometimes just a new gasket fixes the issue. You can also search you tube for ways to test your carb.

 Ps You can take off the flywheel cover. Grab a hold of the flywheel to feel any movement. If you feel any up and down movement, you need new main bearings and seals.