XR-4 continues to rev with throttle closed

[4-mula-V]

I have a XR-4 150 when I rev it up running on the hose, it continues to race at high rpm with carb butterfly’s closed for quite a while afterwards

 

[QBhoy]

I have a XR-4 150 when I rev it up running on the hose, it continues to race at high rpm with carb butterfly’s closed for quite a while afterwards

Unburnt fuel perhaps…or a vacuum leak maybe. Wouldn’t be revving her too much on the hose and neutral though.