I have an Evo S800, S1000 and now a S900 that I bought used

I have a problem with the S900.

When I put the throttle, I hear the sound of the motors that are jerky. As if the gain was too high. If I continue to put the throttle S900 does not stabilize and bank to the side.

I tried to change the gain, but it's the same.

I changed the PMU, the IMU. It remains to change the Controller Unit and motor wire.

The connections of cam1 and cam2 are in the right place.

Does anyone has had this problem?

are you able to post a video maybe?  what are your gains?  what flight controller are you using?  The s900 is a pretty stable craft, I have 11 of them and never had to make any changes to the gain settings.  Everything is left at default.  Perhaps, the person you bought it from made changes on some of the settings.    I would go through the DJI assistant and double check that all the settings are where they should be.  Also are the motors spinning freely when you turn by hand?   Give us more details and we will try to help you as much as we can.