550 Winter Project - 750 Pump Swap and Engine Questions

IceRocket1286

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Location
Metro Detroit
The past few years I have been working out of town during the week and am quite bored at night, especially in the fall and winter. The house I currently rent has a garage so I thought I'd get myself a jet ski project to stay busy and stay away from the TV, so I picked up a 1990 550SX from a friend. I was originally going to buy a 2022 SJ and add a Riva kit to it but I rode one a few weeks ago and it didn't do much for me. The 550 stator needs rebuilding and the electrical box is a mess. Otherwise this was a good running, stock, piston port ski. I believe it has a fairly fresh rebuild but I have not taken the motor apart or checked compression yet. The ski did not have a battery in it but I plan on giving the whole ski a once over this winter so I wasn't too concerned with current numbers. I was going to paint the engine bay white but it is very clean and I will likely give it a scrub down, power wash and leave it at that. Ski is very sun faded. I have some mods I plan on doing but really undecided on engine/exhaust pipe and pump combo. I would like to keep the engine simple, maybe bump the compression and I will advance the timing. Engine currently has intake spacer and SBN carb, unsure of the size. Rev limiter disconnected. I have read through dozens of threads on here and PWCToday and have a good idea of my options. I don't want to build an intense motor but would like to keep it simple enough to utilize the benefits of a 750 pump.

Things I plan on doing to the ski:

  1. Wide tray, Refoam, turf
  2. Pro Watercraft performance front sponsons - Ordered
  3. Pro Watercraft Hull Extensions - Ordered
  4. Pro Watercraft Handlepole
  5. Some type of rear sponsons, remove OEM sponsons
  6. Pump Stuffer
  7. Ride Plate & Intake grate
  8. New OEM graphics or aftermarket
  9. New OEM replica fuel tank from Fly N Ty...gotta love the look of a fresh tank!
  10. Timing Advance
  11. Dual cooling with new through-hull tubes
  12. New motor mounts (suggestions?)
  13. New Hood Seal
  14. Jetski Solutions Stator & Ebox Rebuild (if I go with a 550 engine)
  15. Blowsion Billet Bling
Things I am considering & have questions on:
  1. 750 pump swap - I have a few pumps laying around. This conversion would be fun to do, give performance gains and give me flexibility for future engine setups. BlackMarkit or RHAAS, undecided.
  2. Rebuild Piston Port Motor and run it with Factory half pipe or WAX replica half pipe
    1. How does/would the PP motor perform with the half pipe and potential 750 pump swap? I don't want to overload the motor with the pump/prop
    2. What additional mods would be additional to best utilize the 750 pump swap?
  3. Find & rebuild a reed motor, same questions as above
  4. 750/800 swap
    1. I have plenty of 750/800 twin parts laying around that would make this swap easy to do. I am not a fan of the lack of exhaust pipe options and this is keeping me from saying yes to this
    2. Has anyone utilized the SXR wetpipe manifold/head pipe and made a custom chamber to fit?
  5. 701 Swap
    1. I like the idea of this and that the B-Pipe fits with little modification, but I have plenty of 750/800 twin parts laying around and ZERO yamaha parts so this would be the most expensive route and probably unlikely my choice, but it is a thought.
  6. 2" exhaust tube to replace OEM tube
  7. Aftermarket head to bump compression but run pump gas
  8. Porting only for the purposes of cleaning up casting marks and efficiency
I am currently leaning toward building the PP or a Reed motor to keep things simple. I have a 750SS Electrical box for a conversion, if needed. I also have a single kawi intake manifold as I'd like to keep this engine a single carb no matter what engine I put in it. I just plan on lake riding this ski at home and having fun with it. This is more of a winter project and something fun to do than it is to have another ski. My 800 is just fine for what I need these days.

Any feedback or suggestions are welcome!

1990 550SX.jpg
 
I'd totally skip rebuilding the 550pp engine. Go right to the 750 small pin. With the 750 pump, go with a hooker 10/16. At the end of the day, all the work you put into it, it's still gonna ride like a 550 regardless what you do to it. I went through all of this back in my 550 days. Wide tray, 750 engine, pipe, worked 550 pump. It ran good for what it was but it is still a 550 hull and there are sooo many limitations there. I cut my 550 hull up and did lots of Glasswork only because at that time,550s were dirt cheap. So if I messed it up, finding another hull was pretty easy. The biggest positive to cutting up the 550 was using it to learn to do fiberglass work.
 

IceRocket1286

Site Supporter
Location
Metro Detroit
Thanks for the feedback. I’ve done a few wide tray 550’s and have wayyyy too many hours of fiberglass under my belt. This project is nothing new aside from the 750 engine/pump swap which is why I inquired about what power is best to maximize use of the pump. I still have my SXR’s to ride so I’m not too worried about the handling of the 550, just want something to do to pass the time and jump on the ski on occasion. It’ll also be a good ski for friends & the gf to jump on and watch them struggle

I’ll be bringing my compression tester and some other tools back down to Ohio with me next week when I return for work. Headed home tomorrow for the weekend. The PP motor was pretty fresh if I remember correctly, which is why my friend bought it for his kids. I’ll check it out and go from there as well as inventory my parts stash soon.

Spent a few hours on it tonight, got the tray cut and some foam removed to begin the wide tray process.
 

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I have 3 build threads of my 550 on pwctoday.com if you want some references of doing the job. Might help you on your build. I've definitely used others build threads to help with doing my skis in the past especially withmy most current ski build. The 550 was my first ski and a good ski to learn fiberglass on

1- http://www.pwctoday.com/showthread.php?t=331343&highlight=
2- http://www.pwctoday.com/showthread.php?t=364872&highlight=
3- http://www.pwctoday.com/showthread.php?t=396154&highlight=
 
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