Looks really good!
I am in the same boat, or ski, bought a basically stock 650 that is in good condition and 1 family since new. I haven't even ridden it yet but put all new gaskets and seals in the engine and rebuilt the carb and hope to ride it soon. I want to see how the little 650 does and judge for myself how it is instead of listening to everyone say it is worthless and I need a 701. That being said I already bought a WaveRunner III GP with a 701 and a single ski trailer for $400 and sold the trailer for $300. I am freshening up the 701 and will have it ready to drop in when the time comes.
What does it already have done to it?
The first thing if it is stock is replace the impeller as the aluminum ones are junk. Next I would say handpole spring, intake grate and rideplate.
The 650 has a couple issues that can give you a little free performance increase.
1. The 650 doesn't have a pisser so you can't see if it is getting cooling water and can add too much water to the exhaust. If you Tee into the line coming out of the head into the pipe and dump the water out the side through a "pisser" fitting you can see if it is flowing water but also drying out the exhaust will give a little more power.
2. The 650 bilge siphon system dumps some of the pump pressure out the side for the bilge. You can plug off the fitting then just drill and epoxy a new tube in the nozzle just like the newer skis.
Here is a link to what I did on mine
1980's Superjet?
