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It started with a big gap, every SJ I ever saw has around 3/8" between couplers. I use a 3/16" spacer under each coupler to close the gap.

That 9-17 loads about the same as a 9-15 hooker. The old prop will pull as hard from 15mph to top speed but not out of the hole ( on smooth water). I you have a considerable lag in response then its the engine. The 9-17 is already a light load and buying another impeller wont fix that.

They used that carb for a couple of years on the first 650s. Take it apart and see what it needs, the parts are standard mikuni.

You need to start with an impeller that is close because big hubs are more difficult to work. The load is concentrated at the rear outer edge. Unless you are racing, bore the nozzle first.

All CDK2 have the same body.

The stream fans out more with a straight bore. It will often cause a slight trimming effect and will make the tend to turn, especially if there are no vanes in the nozzle. For freestyle you want the nozzle large for thrust, tapered or not.

It is amazing how long it takes some things to catch on.

Use fiberglass if you can, carbon will eat up the aluminum.

I have been told that Seadoo is up to an 82mm hub. In theory, you could increase the hub until the impeller outlet area matched the nozzle area which would be around 120mm in a 155 pump . As it is, our 75mm hubs allow double the nozzles area. I am curious how well a 100mm hub would work though.

They are opposite of each other. Cool temps make the plugs dark and the pistons clean or with a wet greasy residue. High temps make plugs clean but leave a dark crusty spot on the piston. You should not be looking at these for tuning. This is because they are lagging indicators that can change...

The venturi is the max restriction. If you want to play, cut them out and then spend a day tuning. Or get a pare of 44s, they flow more and are very easy to tune, even OEMs.

The inflowing stream is moving 1/3 as fast as the exit stream. The impeller root angle has to be steep enough not to impede inflowing water. This area is turning too slow to add any thrust, instead it serves only to push water away from the center. Modern ogive hub shape gets the maximum...

The tip speed of the impeller determines the max pressure. Bernoulli the reason we can and should use the largest hub possible. It is common to see 70MPH out of the nozzle. Now, understand that the tip speed of a 144 impeller spinning 7000rpm is 118MPH while the 75mm hub is only going 62MPH, a...

It got a little tight at some point, it is extremely common on watercraft. Not a problem unless it pinches the rings. When it does you will experience a high speed shutdown.

Plug color is a lagging indicator and useless for freestyle tunes because we spend too much time at part throttle. A clean plug at part throttle is too lean for good response.

The pilot and pop off are married and very sensitive around 1/3 open throttle. Small changes to either really show in this range. It needs to be sputtering some for best response. You must power tune the top screw to find the proper main jet. Start 2 turns out and do some acceleration runs...

The problem is labor cost when it has to be lite-weight. It is easy and cheap to design a heavy frame with few fasteners. Look at every panel on a jet.

From a bull builders perspective, any removable hatch is a PIA. It will never happen.

The front seal will always drool a little. I always poured 1/2oz of premix in the cover to keep rust out, plus it turns white if any water does get in.

Even better, how about the entire top deck fastened with 200 small screws for ease of removal?