717 swap with broken 657x

[Jenks13]

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Help swapping 97 gsi engine into a 95 gtx 657x​

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Jenks13​

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Discussion Starter · #1 · 8 h ago

Over the weekend I swapped a good 717 engine from my 97 gsi into my 95 gtx 657x which has a bad crank. The parts I installed from my 657x onto the 717 is the exhaust and dual carbs. I did the dual carbs because I saw where a 97 hx has a 717 with the same dual carbs and that 717 has a main jet 130, the 657x has 132.5, both pilot jets are the same. I did get it to crank and it seems to idle and throttle up fine (out of water) but need advice on running the water lines. I've also seen in a repair manual where a typical 717 has a very similar cylinder head cover but my 717 seems to have a typical 787 cover according to these images. So can anyone help with personal experience doing this?

 

[mikidymac]

Parts are not interchangeable between the 657X and the 720.
Even the carbs are different.

If you are going to run a 720 you need everything from the 720 from the carbs to the electrical box.

 

[Jenks13]

Parts are not interchangeable between the 657X and the 720.
Even the carbs are different.

If you are going to run a 720 you need everything from the 720 from the carbs to the electrical box.

Your saying they aren't interchangeable but like I mentioned I found the 97 HX 717 engine actually does have the same dual carbs. There's also another 717 that has the same carbs also so they must be somewhat interchangeable. I also have it running right now on the 657x mpem.
Have you ever swapped a 717 for 657x? I need someone with first hand experience who's successfully done a swap.

 

[mikidymac]

657X was it’s own strange beast and the carbs were mounted inline instead of sideways like the 720. And the mpem timing is going to be a little different.

If you are still set on doing set everything to the 720 specs, jetting, screws, needles and seats.

Don’t change head covers, 657x 720 and 787 are not the same. Just plump cooling lines per a 720 engine diagram.

 

[AKnarrowback]

There is a huge difference between having a motor run and having a motor run right.

Changing the ignition system between different motors is not suggested. Things may fire off, but the rest of the timing curve probably doesn't match up and might cause motor damage. Or it might work good enough, but you are gambling with your motor.

As stated, the 657x motor was was only used for two years in a few select machines. It has many original design aspects that make it so even the 657x will not interchange with the 657 motor.

The need to have done this specific swap is not required to offer practical knowledge. We are just offering up a suggestion to your question based on our knowledge of sea-doos and small engines.

"Group K" has a couple of papers, in their website information tab, that can give you some insight into how the SBN carbs can interact with other machine aspects and cause engine damage in certain situations.

Or maybe your swap will work just fine. Let us know how it turns out, I'd be interested to know.

 

[Jenks13]

I took it out for about 2 hrs Thursday and it ran great. I brought a laser temp gun and kept checking the temperatures on the head and exhaust and this compared to my 97 gsi they were both within 10 gegrees of each other. I found another 717 ski that uses the same carbs and timing so technically they should work. So in summary I'm running a 717 top and bottom end, 717 upper exhaust piece, 657x muffler, 657x dual carbs, 657x electronics, 657x jet pump all in a 95 gtx hull and so far it runs just like before. Next time I go to the lake I'll take a video

 

[Jenks13]

Here's a short video of me riding the skibwith my son. Like I said it's got the 657x electronics, jetpump, dual carbs, and muffler with theb 717 engine and exhaust. Runs great and we ran it for about 2 hrs. Engine has roughly 142 psi on both cylinders and takes off.

 

[etemplet]

Like the Cajuns say down here. "Dat's Money!!" LOL Great Job !!