Lower unit jumps up in reverse

[James Waters]

How can I lock down a F 70 A Yamaha w/ power tilt and trim to prevent it from jumping out of the water. I drift the river a lot and I have to quickly back up sometimes to avoid obstacles. I cannot see any way to lock it down. the tilt and trim works fine, just cannot lock it for reverse.

 

[nccatfisher]

You can't, the lock is controlled by the hydraulics on the tilt/trim. When you are quickly backing up the power of the motor is overriding the power of the tilt/trim. If it is riding completely out of the water you have a trim/tilt issue. The hydraulics aren't strong enough.

 

[James Waters]

Thanks nccatfisher! I just bought the boat. The tilt and trim goes all the way up and down smooth and quite. Still there is the possibility that I was trying to go backward too fast or that the hydraulic fluid may be low.