My GS motor is a no go, need some advice

[AJF22]

I took my 2001 GS out over the weekend (720cc) and on Saturday after about 20 minutes the motor made a vibrating noise and what sounded like some knocking, then turned into a squeal. I went back to the dock and ran it on the hose, no sounds but I noticed I didn't latch my breather box lid on well, so it was laying against the hull and bottom end of the box. Thinking that was part of the problem, the knocking, I went home and checked everything. The spark plugs looked good, I didn't see the shaft was misaligned or had a bend in it and it ran great on the hose, not one problem.

The next day I took it back out and cruised around for 20 minutes between 4000 and 6000 rpms, then went outside of the harbor to do some WOT runs. All was good for about 30 minutes and then the motor lost some power, so I turned and headed for the nearest dock. I knew the motor was going to shit out on me and I knew there was no way I was going to make the mile and a half trip to the ramp. Then shortly after it lost some power, the motor seized up on me and wouldn’t start, so I paddle a quarter of a mile to the dock where I waited for harbor patrol to tow me to the ramp.

Here's a video where you can hear and see what was going on with my ski:

When I got home, I pulled the head covers off to see if there's any visible damage to the cylinders, everything looked good, but I could only see the MAG side as the PTO side was stuck top dead. I want to manually crank it around, but I don't want to disassemble it just yet till I get some information on what direction I should go and make a plan.

I read on here that it could be the jet pump seized so I’m thinking of maybe disconnecting that first? Hopefully it is just that, but I'm sure it's not.
If it's a blow motor, which I’m sure it is, I do have a parts ski, but it's a 94 SPX with a 650 motor. I'm wondering if it’s possible to swap that motor for the GS motor, is that possible?
Also if the jet pump is bad, will the one on the 94 SPX fit on my 01 GS?

A little background on the motor:
It had 150 psi on both cylinders.
I rebuilt the carb with a Mikuni kit.
New spark plugs.
Spark plugs looked normal for a 2 stroke after the first ride.
After the engine seized, the plugs looked brand new, I should have run premix instead of trusting the oil pump. Rule #1 when it comes to Johnson/Evinrude outboards (BRP), remove the VRO and do premix.

Thanks

 

[burtshaver2021]

Start with compression test, if it’s bad check your oil lines and pump arm alignment, if they are good pressure test the crankcase for air leaks, you may have ran lean from not having the air box on, ( less air restriction) or you may have invested some water, either way check compression first

 

[burtshaver2021]

Sorry, I didn’t see the test of your post before I replied. You will have to wait for someone much more experience to reply to answers the questions you have, in my humble opinion trying to put the 657 in the GS wouldn’t be worth the effort and I would think there would be some difficult modifications needed like glass work for the mounts, probably need the electrical from the donor as well. See if someone can give you a better answer

 

[AJF22]

Thank you for your reply.
Regarding a motor swap, the SPX I have is a complete ski with the e box, but mounting the motor from the SPX in the GS is a big question I have. It looks like it is possible, but looking at the exhaust pipe might be an issue with mounting the motor, but I have no clue if there is a way to mount everything.
I’ve seen a thread where a guy asked a similar question, but it went cold after a reply was left saying, the e box for the 720 would work for the 650, but it will not work the other way around. So that raised a second question, can the e box from my GS 720 work if somehow the 650 happens to be able to be dropped in?
If the motor is able to be dropped in, swapping the e boxes shouldn’t be to big of an issue if needed.
The 650 I got for free and the PO, a Hollywood production company that bought it for shoot, has no information on the PO they bought it from. To me it looks like the top end might have been rebuilt and it looks like the carbs were rebuilt too. The compression on the 650 is 150 per cylinder.

 

[mikidymac]

Pull the pump before you do anything.
It could be a seized pump and it needs to be pulled before the engine anyways.

 

[AJF22]

I worked on the ski this evening and found out my motor is good which was awesome to find out, but the jet pump was locked up. The inside had broken pieces of metal falling out and it smells like a 20 year old cigarette ashtray. I also noticed there was water in there and it looks like the PO never changed the oil, should have not took his word that he did change it when I bought it, live and learn is what I'm doing as I'm new to PWC's.
Now it’s on to rebuilding the pump.