There should be an adjustment on the back of the tach, it may not be set up correctly. They are designed to be used with most engines, but I don't know which setting it is for 4-stroke, maybe someone else can help out there, if not call a dealer service department you trust. Tach could be bad, could have a bad connection. When I had the Teleflex analog tach on mine when the engine was shut off it would read what rpm it was at when it shut down. Soon as I turned the key it would drop to 0.
EFI is all ecm controlled, no adjustments that I know of. It should also have a rev limiter to protect from over rev.
(Don't know your history with jets, if you're new to them maybe this will help.)
When you take off, starting out of the hole have the engine trimmed down, when you start gaining speed and the bow starts coming down start trimming up. Once on plane the engine should be close to level, you'll know when you hit the sweet spot. When it starts to porpoise or if it cavitates bump the trim down a few times till it stops. If you keep it trimmed under on plane the bow is plowing water and the shoe is dragging slowing you down.
Also as eli2 mentioned check the mounting height. Do this by taking a straight edge (yardstick, board, angle, or whatever you have handy) and place it level on the bottom of the hull and extend it out to the shoe. It should hit the shoe somewhere between the leading edge and the pin that holds the grates in with the engine trimmed down. Also check throughout the trim range until engine is level. If the leading edge of the shoe drops below the straight edge then its dragging, slowing you down and probably has a lot of backsplash at the transom. If this is the case it needs raised.
Good luck, hope this helps!!!
