First try at mud motor. Gained more insight from MMT than any other source. Started with cav plate flat but could keep in water above 1/2 throttle. Bent trailing edge up with same results. See attached pics. Do I need to move further down tube? Thanks for any help!

It's kinda hard to tell from the angle of your picture, but yes I would say you need to move the plate closer to the prop. I've have had better luck changing the angle of the plate instead of bending the trailing edge.

If you can't keep prop in the water then you are creating too much lift and not enough down pressure. The down pressure is caused by having a steeper angle on the cavitation plate, the water flowing over the top pushes it down counteracting the lift cause by the prop. Get a piece of 1/4" aluminum the width of your cav plate break it in half with a slight bend and bolt it to the cav plate. This will allow you to bend the trailing edge up to create more down pressure. It also allows you to replace it instead of bending the crap out of your welded on cav plate. Good luck

Here's another picture I couldn't get to post earlier.

From that angle it doesn't look too bad. It wouldn't hurt to be back over the prop a little more. But
I think you trouble is the side wings are casing turbulance at the prop. Your plate is wide enough, I would cut the side wings off or at least bend then up some and try it.

I put a cavitation kit from Backwater on my MB, what a difference! Big improvement.

Just a thought (speaking from my own experience) I found the flanges that bend down on the side of the cav plate to cause excessive lift. I know the main purpose of the plate is to keep water surrounding prop. I also realize a lot of manufactures have them. I am assuming they add rigidity and in theory to act as little rudders. On my build I cut them off and it solved my problem. (the same problem you are dealing with)

My cav plate is narrow, triangular, with the end sightly for fine tuning. It almost seemed like the upside down U was a catch for the water creating lift. I see yours is a bolt on... If your willing to test my theory flip it over, and flatten the tab on the back. See it it then "catches" the water above it, reversing the current lift resulting in down force.

I think I'm gonna make another plate a little longer than first and leave it without fins. I made it bolt on in case I needed to modify. Thanks