Custom/Hybrid Kawasaki js300/750 swap to a 300sx hulll

[Austindib]

Hello all! First post here, not new at stand ups but new to swaps and heavily modifying them. I currently have a js300 with a big pin 750 swap and a 550 pump. I’m looking to pick up an sx300 hull and partial flat deck it with footholds for all of the freestyle fun. Assuming that they came with the same motors, the driveline swap should be pretty cookie cutter given that the 750 is already in a cradle that’s in a 300 hull? My js is side exit exhaust , what recommendations would be had for the exhaust in the sx hull? Thanks! I’ll have update pictures along the thread as I’m picking the hull up sometime in the next week

 

[mthomps]

You might be opening up a huge can of worms.

From what I can remember the hulls are completely different. Engine mounts are different. Sx hull won't except 550 pump without modification. Exhaust exits out the rear. (From what I remember)

The 300sx hull is better than the js300 hull but transferring your driveline over won't be bolt on and go. Also the 300sx isn't a very good freestyle hull.

You might want to consider finding an EME hull set up for kawi instead

 

[SexPanther]

I don’t think flat decking is functional either. A widened tray with foot straps though is super functional. I think you should keep that hull because it is awesome!
Here is what I would do. First 750 big pump conversion. It will give you the bottom end hook up you need for tricks. RHAAS and Blackmarkit both make kits that bolt in and use an x2 driveline.
Second adjustable aftermarket handle pole with over pivot steering. In my opinion best modification for any jetski. Being able to personalize your pole length is a game changer. And OVP is the best thing ever.
Third widen that tray up. RSKI Riders on YouTube is about to do a video on tray widening. A bigger dance floor is always better.
At this point your ski will be a masterpiece. You already have the big power plant swapped in so you are almost there! Just my 102 cents.

 

[SexPanther]

Sx and Js have different pumps, driveline, bulkhead pass(sx rubber carrier bearing vs midshaft thing in js), sx is rear exhaust, and sx has rear sponsons which basically should be removed anyway. I don’t think there is any technological advantage hull wise to sx. Also I left out in my last post, Fish Stix or pro watercraft rear sponsons. So amazing literally makes it ride like modern skis. That should probably be #1 actually. And tubbies!!! Front sponsons are also a total game changer on these skis!

 

[kevbo]

A "game" changer? Whats your game, I found tubbies good for turning at higher speeds and worse everywhere else.

 

[mthomps]

We mod to get the specific experience we desire. If that's turning really fast so be it.

Welp OP decide what your game is. You said freestyle..so do you want to spend 100 hrs modding a 300sx or ride a freestyle hull? That's it really, in my opinion.

If you'd prefer riding and learning freestyle abort this project and drop whatever your best driveline is into an actual freestyle hull and ride it.

If you prefer cutting, sculpting, sanding, glassing, repeat repeat for the sake of it to make what you want do that. That's how freestyle was invented after all.

 

[SexPanther]

A "game" changer? Whats your game, I found tubbies good for turning at higher speeds and worse everywhere else.

What else do JS hulls really do besides turn? And what was a ski with tubbies specifically worse at doing? I think they make it easier to get the turn initiated, at any speed.

I guess the next question is what do you all mean by freestyle? Like fish walking in your tray, riding backwards on your hood, headstands in the tray, and subbing under log booms? If thats the case any ski can work.

If by freestyle you mean one of those short little flipper boats that would kill your back to ride in a straight line to the other side of a river.. I'm not sure where I would start with the parts you have. Almost all of those hulls run Yamaha drivetrain, require an aftermarket pole, and a whole myriad of other parts to build.

So my suggestions were how to make the platform you have a good ski that will be fun everywhere. If you are trying to do a flat water backflip off your own wake... It's going to be about 10x as expensive as doing everything I suggested and you will have a ski that literally does one thing well and is terrible at everything else.

 

[UKUnicorn]

Yes its more money to buy an aftermarket hull but as mthomps said youd be much better off looking for an EME kawi freestyle hull as you will spent alot of hours building your own hull for freestyle, that being said I guess its up to you what you want to do but IMO tray time is more valuable than anything else and you won't get much when building your own hull. Just my opinion.

 

[mthomps]

What else do JS hulls really do besides turn? And what was a ski with tubbies specifically worse

I guess the next question is what do you all mean by freestyle? Like fish walking in your tray, riding backwards on your hood, headstands in the tray, and subbing under log booms? If thats the case any ski can work.

If by freestyle you mean one of those short little flipper boats that would kill your back to ride in a straight line to the other side of a river.. I'm not sure where I would start with the parts you have. Almost all of those hulls run Yamaha drivetrain, require an aftermarket pole, and a whole myriad of other parts to build.

So my suggestions were how to make the platform you have a good ski that will be fun everywhere. If you are trying to do a flat water backflip off your own wake... It's going to be about 10x as expensive as doing everything I suggested and you will have a ski that literally does one thing well and is terrible at everything else.

If you want to have fun everywhere you forget all this, sell your stuff, buy an old waterlogged pig of a superjet. Same for old school freestyle.

Every single 300sx freestyle build posted has been sold off to either start over (with a superjet as the base) or for money towards an aftermarket hull. I think the BOB hull was somewhat 300sx based. (Nobody kept them)

Where he would start with his driveline for freestyle is to look in to finding an EME freestyle hull which were designed for kawi and had conversion kits for yamaha.

I'm not saying any option is better than the other. I have a 300sx hull that I learned to ride on. It's a fun little piece of crap but it's in fact a piece of crap.

I'm only posting to give op info to make their own choice on what to do

 

[SexPanther]

No doubt old waterlogged superjets are superior craft to JS hulls, and also not in the same price range. But a JS hull with a 750 swapped in is a solid ski. Not sure what his current pump is, but if you deliver that power to a decent pump it could be a really fun ski.