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Most expensive oils have some technical merit, just not economical for freestyling. Remember that jetskiers, for the most part, are athletes. They interface the world via their five senses, smell plays a major part of oil purchasing decisions.

SN Superjets were so poorly built that you are lucky if all the hardware is even there.

Power potential is about the same providing an equal quality pipe is used. Going forward the Yamaha will be easier to support. I still have a sweet 750 engine but its my last one because of parts prices/availability.

The bottom should be blasted and the top polished. The gain is so small, at best, that fine instrumentation would be required to measure. They make them rough because its cheaper.

Good ole hose clamps are way too expensive for cheap ass OEMs. A lot of hose clamps will unscrew under engine vibration. Hard to beat a big nylon zip-tie.

There is no tuning effect with the stock Superjet pipe. It is the one and only exhaust system that will benefit from a free flowing waterbox. Problem is that we cannot turn enough rpm to make up for not having a tuned pipe no matter what else is done. So basically messing with the stock exhaust...

You need a 650 Nozzle.

It going to end up about as well as "do it yourself" heart surgery. His questions were the equivalent of "what kind of knife should I use" and "how do I keep the patient from crying"?

Best oil for what application? It turns out that the best oil for puttering around and dunking our skis just happens to be the cheapest and most available, TCW-3. Sitdowns and racers do better with an air-cooled spec.

A 750 needs the exhaust outlet on the R/H side to keep the engine from filling with water when its laying on its left side in the water. The 650 can have its exhaust outlet on the left because it has a long stand pipe in the waterbox to keep water from pouring into the engine.

Its an expensive mod for what you get. You need 44s to make it worth doing.

Pass on any old ski unless its perfect and/or has all the expensive goodies. The old Kawasaki 650-750 can do some things better than a Superjet but nobody rides that way anymore. Yamahas have more going for them and are a better choice overall.

You have to become your own "pro". Unfortunately it is an expensive process involving a lot of time and melted pistons. Its worth learning if you are in the game for many years.

You really have to disregard 90% of of the used items being sold by any motorsports enthusiast. If you cannot get a dozen high definition pics and a return policy then the person is just offloading junk and they know it.

If all things are equal then just shoot for 30% more area. Pilot jets are much easier to predict because the vacuum signal is always similar between all sizes of carbs at low throttle openings. With this variable out of the way you can figure (more/less) a direct line between butterfly diameter...

I always found a direct trade-off between power and response when going from 178-186-192 degree port height. Can you get enough power with an ultra low port?

Mikuni round main jets and keihin CDK mains are sized in MM, a 150 main = 1.5mm hole. Older mikuni hex mains are based on flow rather than size. They provide more linear progression that is easier to work with in smaller sizes. Pilot jet numbers seem to be proprietary between brands and styles...

Here is one trick I discovered that works very well for keeping water out of the vent line. Run the end of the vent line half way into a small bottle or can (asprin bottle) and poke a hole at the bottom and top with a needle. Air can pass easily enough while water entry is cut way down. It buys...

Use an 92-95 SX cylinder.

The dome size between the 650 and 701 are nearly the same, the 650s exhaust port is lower creating equal trapped volume. I would find a 650 head/gasket or a 64u head from a newer 701 with a 62T gasket.