Decrease in acceleration during 2500 to 3500 RPM

[nabeelmech1]

I have Cultus 2007 carby. There is no problem in neutral gear, engine's RPM increases smoothly from 1000 to 5000. When I drive it in any gear, it accelerates smoothly from 1000 to around 2500. However, on increasing beyond 2500 to 3500, it feels like car is running with reduced acceleration. After approaching 3500 and increasing beyond it, car accelerates smoothly.

In short, there is an abrupt loss in acceleration from 2500 to 3500. What could be the possible problems with it?

[hassantahir2]

Check if the secondary throttle butterfly is operating smoothly if there is some sort of delay only then this problem happens.

[usman_arooq2]

also could be timing advance not working properly, check for vacuum leaks.