my son has a boat with a 1999 Johnson 115. when you lower the motor motor starts to bouncing down. it goes up just fine just when it your lowring it. as I raised and lowered it. it back a little smother. but still bounced. any one know who might be causing it. I would post a video but I dont know how

My 150 does it on the trailer till it hits the trim rods but I don’t feel it at all in the water. I know that’s not a answer but It’s done it 10 years and still working.

That could be due to air in the hydraulics. Have you checked the hydraulic fluid level? Be aware that the engine should be in a particular position when you check the level. If I remember correctly, it should have the trailering brace lowered and in position with the engine trimmed to snug it in place. The owner's manual will tell you the procedure. If you don't have one, look for one on the Internet. If it needs fluid, buy a tube of it from a dealer. The squeeze tube makes adding some easy.

It could be fluid. It could be that the pivot bushings are worn. I just replaced the pivot bushings in a Yamaha 225 because it seemed to be kinda jerky. What I found was the pivot bushings were worn and the thru shaft they mount on had a loose bolt, which probably led to the worn bushings. They were very easy to change and cost was nominal.

Wayne