To really understand how these boats work might solve a lot of your questions. The basic concept of jet boats is jet propulsion. Normal prop boats use an external prop to push the boat along. Jet boats use an internal impeller. Think of it like a big fan blade. It sucks water up through the bottom of the boat and pushes it out the back through a smaller opening, creating force and moving the boat. That is the basic concept. When there is a restriction to the water flow, this thrust is greatly reduced. If there is a leak anywhere on the outlet side of the impeller, you get no thrust. This loss of thrust is called cavitation.
1. The intake on the bottom of the boat can become clogged up with weeds, sticks, and other debris. When this happens, the impeller no longer has water coming through it and therefore you have no thrust to move. The weedless lever is a grate that looks like fingers that covers the intake. When you pull it, it pushes the fingers down, hopefully removing the obstacle blocking water flow. Best way to use it is to stop the boat, put it in reverse. Pull the handle while you go in reverse moving the wheel back and forth. Usually works for me.
2. It should be very fast to get up on a plane. Faster than a lot of other boats. If it feels like something slipping, you may be experiencing cavitation. Could be something as simple as needing a new wear ring. A wear ring is like a gasket the incases the impeller.
3. First step was finding this site. Now you need to read, read, read. When that is done, read some more. The search feature works great.
I am still fairly new to these boats, but this website is a wealth of knowledge. These boats are really basic once you figure them out. Welcome!!!