If you want to get the most out of your Berkeley 6JA Jet Pump, then you need to improve its efficiency.  The intake 5 fin intake grate is very restrictive to waterflow.  Not only is it restrictive, but the fins are flat where they face the water.  This "un-aerodynamic" edge creates a tremendous amount of water turbulence going into the pump.  The more water you can get into and through the pump, the more force it will produce.  Of course the horsepower of the engine and bit of the impeller come into play as well, but any improvement....up to the point at which the engine can't power it, or the impeller can't move it....is still an improvement.

• First, cut out 2 of the fins on the intake grate.
• Next, use a die-grinder with a coarse bit designed for aluminum and grind the top and bottom edges of the fins so they are very airfoil shaped...like an airplane wing in cross-section
• Next, put a 3/8" radius on the back curvature of the grate where there is currently a sharp wedge shaped edge.

Note the difference in the "before" and "after" pictures!

• My suggestion would be to use Marine grade gear oil, especially synthetics.  I'm using the 85/90w oil in mine. 
• Fill the cavity that's under both of the red screw in caps in the photo below.  The cavity nearest the engine is the actual bearing, with a seal on either side.  The cavity nearest the stern is just a set of seals to keep water out and protect the bearing.
• Some marine places that service Berkeley Jet Pumps will suggest using marine grade grease.  I think that works well too.  I decided to use gear oil instead, because I wanted something that would flow and circulate around the bearing.  My thinking is that grease is thicks, so there's some drag on the pump that takes horsepower to overcome, and grease doesn't circulate, so your bearing is always running in the same bit of grease.  Maybe that's not correct, but that's my thinking for now.
• There is one other lubrication point out where the pump shaft rides in the tail housing of the pump.  If you look into the back end of the pump you'll see another screw-in plug there in the center of the Stator.  Lift the rear of the Sea Doo 3' higher, so you can pour marine grade gear oil into the tail shaft bushing.  Then replace the plug. Alternatively, you could remove the pump nozzle and bowl/stator housing and put marine grade grease inside the bushing, and then slide the stator back on and reassemble.
• It's a good idea to check the oil or grease (which ever you're using) levels every couple of rides depending on how long you go out for.  It would be a shame to burn up a bearing or tail shaft bushing do to a lack of oil.