300/440/550 440 Aftermarket Exhaust Manifold and pipe on 550?

[Freakshow]

Hey everyone, I'm sure this has been covered but I haven't had any luck searching for it. Had an 83 JS550 and a JS300 hull fall into my lap. The 550 is pretty much 100% stock and complete and the 300 hull is minty fresh. I want to get some more performance out of the 550 but not trying to break the bank too badly as I'm trying to get the 300 built and running as well.

So far it seems the must do mods are
Quick Steer (couldn't agree more lmao)
4* Handlebars
Ride Plate
Impeller
Shim/blueprint the pump
High Comp Head
Being an 83 it has the BN38 on it, so a S/BN44?


And that leaves exhaust, has the early style on it, not the jet power. I know everyone says jet power with the factory half pipe but thats going to cost more than the ski itself did. So what I'm wondering is, would an aftermarket exhaust manifold like an L&S with a full pipe like west coast, coffman, kerker etc be better than my stock setup? Would it be better than a fully stock jet power set up?

The 550 came with a spare motor so I took the head and milled it. Static compression is 150psi right now. I'll probably take a little more off, shooting for 170psi or so. The guy I bought it from was a goober and recently did the top end. I doubt he gapped the rings so I'll be tearing down to check. Figure I'll do some mild porting while I'm in there.


The setup will likely end up being a 15* SS impeller, a 44mm carb, the porting and hi comp head, plus whatever exhaust set up I go with. It'll be used in a mile wide river or the ocean, so the water will rarely be particularly smooth so I'm not really looking to go 50mph. I want to retain reliability and the bottom end and whatever I can get up top is a bonus. I haven't really rode since I was a preteen but I've been out with it a couple times now in 1'-2' chop and the skills are coming back quickly.

As far as the carb, would the SBN44 be a big improvement over just a BN44 on this build that will be pretty mild or should I just get someone's BN44 pull off? Has anyone tried the SBN clones from aliexpress? I've had good luck with china carbs on my moped builds but these are quite different beasts.


Thanks everyone.


Everyone loves pictures


I know the trailer setup is a little janky still, but I finished welding up my hitch yesterday and the weather was too nice not to brap

 

[WFO Speedracer]

Any of those pipes would probably be an improvement over the 83 style exhaust pipe.

 

[Freakshow]

So I scooped a Jetsport 440 pipe, looks to be a west coast copy. Probably paid too much but its in great shape and I wanted it. Also have an ocjs exhaust manifold on the way.

I ended up just making a quick steer plate to add on to the stock setup, dremeled the steering nozzle a little bit for increased throw and actually got the steering pretty well centered and wow what a difference. The middle 50% of the steering actually does something now and the increased throw is really nice to have. Tried to swap the straighter bars from my 300 onto the 550 but damn some of those screws were mad stuck and the heads of those phillips screws are as soft as cheese. Even using an impact screwdriver I could only get 3/4 loose on the stop/start switch and couldn't get the one on my throttle to even budge a little bit. So I decided to save the drilling and extracting adventure for another day.

Currently on the hunt for a good stainless impeller, a ride plate and an intake grate, but we're getting there.



Been out for a rip a couple times since my last post, had some smooth water to work on the basics. Still very much a scrub, but I'm getting there.

 

[Myself]

Very nice. Looks like you've got it running well.

 

[Freakshow]

Crazy how dead this forum is but,


I bought a 440 a couple weeks back, kerker header and pipe, the blowby was horrible when I first took it out but runs really well. Stock impeller was chewed all to poop, definitely quite a few large rocks went through it. Filed it best I could with it still in the pump and it made it a good bit better. Got an unknown brand 17* stainless impeller and wow what a difference. It feels over propped but the holehot is so much better and it GPS'd 37 and change but it'll do better.

Figured out I had been running the wrong plugs in the 550 the whole time. Explains why its been really difficult to start. I bought it with B7HS's in it and thought "great, I already have a dozen for my moped" and then never looked into it further. The 440 came with B8ES's in it and then I had a lightbulb moment. Having a plug thats 1cm too short sure causes some issues.

Got an ocjs ride plate on the 550 and an ocean pro on the 440 and I much prefer how the 440 rides. I'm sure its mostly the sponsons on the 550, but the difference is a lot bigger than I thought it would be.

I havent installed he pipe and manifold on the 550 yet but its coming soon. Looking for a 15* impeller too.


All in all having a bunch of fun. The 440 is a serious ripper. My girlfriend is standing up and turning figure 8's. I just have to remember to reapply my sunscreen.

 

[Myself]

Yay!! Good times for all! And good exercise too.

 

[Freakshow]

Good times and crazy good exercise. Also having fun making all the tools

 

[Myself]

Just be careful, we don't want to read about you in the funny pages.

"Florida man.....loses thumb while using homemade impeller tool" !!!!!

 

[Freakshow]

Put the Jetsport pipe and OCJS manifold on the 550 and wow what a difference. I cleaned up the stock impeller too and it did 35. Its running much better all around. Scooped a BN44 and a mariner manifold for it and looking like I'll have a 15.5* impeller for it too. Should hopefully keep up with the 440 at some point.

Put an LS manifold and a modified stock intake on the 440 but havent ridden it yet. Will hopefully be good for a little something something.

I got a parts motor with the 550 when I bought it and I finally got around to pulling and really looking at the cylinder. Its crusty but in pretty good shape and only at stock bore. I figure I'll give it a mild port job and put it in the 550 when I get around to doing the crank seals. I also split the cases on the spare motor just to see what I was in for and it couldn't have been easier. The center crank bearings are pretty trashed but might not hurt to have a completely gone through bottom end.

 

[Freakshow]

Still have all both of my thumbs too

 

[fastgtfairlane]

Get your reduction nozzle bored out on both pumps while you have the pumps out. I think you can safely go to 68-69mm on the 440 and 550 pumps. Stick with a half pipe setup with the 550 pump. The 550 pumps load the engine hard at lower rpm and the shorter 440 full pipe doesn't generate enough torque for the 550 pump so you'll end up hitting a rpm wall wher the engine just won't rev out unless you unload the pump then stay in it. That is why racers preferred the 440 pumps over the 550 pumps.

 

[Freakshow]

After four years I finally caught the covid so time for a long post...

The reduction nozzle boring is definitely on the list, I also got a spare stator for my 550 pump that I'm going to rebuild and blueprint because I'm missing some chunks of stator vanes on the installed one. I restore cars for a living and have a well stocked home shop with a cheap mill, but no lathe, and I still haven't come up with a good way to do the reduction nozzle boring at home if anyone has some suggestions.

I'm definitely aware of how the 550 pump loads up, in concept anyway. I also know everyone loves the factory half pipe with the 550 pump. My 550 is unfortunately an 83 so it had that weird in between exhaust setup before the jet power. I know the 440 jetsport pipe and OCJS manifold setup isnt ideal for a 550 pump, but I can't stress enough how much better it is than the stocker was. It starts much much easier and performance is much improved. I also bought a foot of aluminum tubing that matches the ID and OD of the jet sport pipe so I can play with the tuned length and see what I can get there. I'm new to modifying jet skis but I've been playing with mopeds for years (got my little 49cc spinning 10k rpms and going 53mph mostly by modifying stock parts and fabrication) and all the port timing, scavenging and pipe theory etc seems to transfer over pretty congruently so I'm at least working with some base amount of knowledge besides "bolt on parts and go faster."

I really wanted a 14.5* impeller for the 550 but I did end up scoring that 15.5 for $90. Figure I can repitch it myself or have it done and still be ahead money wise. Same for the 17* in my 440 right now.

I also got a china clone top loader intake grate and put it on the 550. It was a pretty rough casting and needed a good bit of milling to fit well but it was mad cheap so I won't feel bad when I hack it up later. Seemed to help with hook up in chop but haven't tested the impact on speed because conditions have been choppy. I'm running a homemade intake "chip," like the one ocean pro made, on the 440. One of these days I'll swap them and get some A/B data.

I also plan to make a pair of intake tract stuffers out of HPDE cutting boards or something similar next time I have the pump off one of them. Needing two I don't want to spend the money on the pro watercraft ones or the time fairing them out the old fashioned way. Might be a waste of time but I think with some CAD (cardboard aided design) I should be able to make a good pattern pretty quickly.

Still trying to decide what to do with the JS300 hull. Torn between building up a nice 550 engine and slapping it in there or something a little more wild. Time will tell.

Does anyone offer a remanufactured crankshaft besides BST?

 

[fastgtfairlane]

You can use a milling machine to bore a nozzle as well just takes a little more setup time.

I had a 750 engine in my 550 at one time with a 650sx Westcoast pipe which is very similar to the jetsport pipe. It had a 4.75in OD. I found a piece of 5in od- .125 thickness aluminum pipe and welded it to the Westcoast pipe. Basically making it 3 inches longer and increased the volume a little. It made the pipe really come to life. You should be able to do do something similar with the jetsport pipe.

Competitive crankshaft I know rebuilds 550 cranks. They do excellent work. Had them rebuild a 550 crankshaft for me years ago.

 

[Freakshow]

I shouldve been a little more specific, I have a very beefy drill press with a milling table and vise installed and I'm by no means a machinist. Any thoughts on how you would do it on my "mill"?

And I just checked my emails and I bought 4.50" OD with .125" wall for 4.25" ID. There's maybe 0.5-0.8mm of a lip from ID mismatch but for $31 per foot delivered I was pretty happy. Glad to hear your experience aligns with what I was thinking. Hopefully the 550 wants some extra chamber volume and it just might work out.

And thanks for the suggestion, seeing how crusty this crankshaft is makes me wonder what they may look like in my two runners. Fresh bearings, crank seals and whatever you call the center seal with a dowel pin would make me feel better once I start some porting and making real power.

 

[Myself]

Just get a cheapo flycutter and a piece of tool steel. Set it up and spin the drill by hand until you know it's centered. Adjust the cutter out a tiny bit and cut! Then again..........I have a real mill LOL!

 

[fastgtfairlane]

As stated above you can clamp the nozzle to the table, and use a boring head. Or if you have a vice you can make a fixture that clamps in your vice that you can bolt the nozzle to.. there's many videos on YouTube on how to make your own boring head or fly cutter. Fly cutter will work just as well. I believe the stock nozzle is 64 or 65mm. You can go to 68 or 69mm safely. Every nozzle will be slightly different because of the casting.. your drill press/mill will work fine for the nozzles since they're aluminum. Definitely want to take the time and indicate the spindle to the nozzle bore to get it as centered as possible. And as stated in the last post, tool steel is cheap and will work great with the aluminum. Plus you can sharpen it with a basic bench grinder.

 

[Freakshow]

Ahh good call on the fly cutter, that'll do the trick, cheaply. I should be able to just T bolt the nozzle onto my table, but a fixture for the vice is really doable if not. Thanks for the suggestions.



There's a 750 swapped 550 "near" me and the guy says he'll do $1500 but I think he'll go lower. I'm trying to come up with reasons not to buy it but I can't think of anything...



Scored a bn44 and west coast flame arrestor for the 550 (and 550sx manifold and reeds) for $100. They were both pretty crusty but cleaned up nicely. Should work well with the Mariner manifold I've got. I think I might finally redo the crank seals and inspect the crank while I'm in there. I have a feeling its a ticking time bomb but hopefully not. Good to know either way. And if I'm gonna do the seals I might as well have a ported cylinder ready to swap on. Covid kept me off the water this weekend so might as well turn some wrenches.

 

[Freakshow]

Finally put my spare cylinder in the blaster and got it cleaned up. Wish I took a before picture because of how crusty it was, but its squeaky clean now. Started cleaning up the mouth of the transfer ports and getting the boogers out. Going to raise the exhaust ports a couple millimeters, lower the intake 1.5mm, widen both a couple millimeters and leave the transfers alone. I'm planning on keeping the round profile to keep the bulk of the port time area close to stock but increase how much this thing can breathe and hopefully pick up some rpms on the top. Seems like there are a lot of gains to be made just cleaning up the runners so hopefully this will all go well.

I'll probably pull the engine at the beginning of next week so I can replace the crank seals and inspect the crank. If all looks well I'll swap cylinders but if the crank is questionable I'll reassemble with the stock port cylinder. I would then order a reman crank and put it and the ported cylinder in my spare cases and do the swap later on.

 

[Freakshow]

Ended up scooping the 750 swap, don't have it running right yet. but its had a few moments where it really pulls. Its a 750sp from an ss-xi as best I can tell. Dual 3 jet CDK's, a coffman pipe from a 650, stainless prop of unknown pitch, but seems pretty well suited to the powerplant. Also has an aftermarket waterbox with the low right side exhaust outlet and holy balls is it loud. It thankfully doesn't carry but I'm really hoping I can stuff a stock waterbox in the for now and then ultimately go rear exhaust.

Initially I thought I had a carburation issue (quite sure I did), but I've rebuilt them both, checked the pop off and all that and I've still got a misfire just about everywhere so I think it was a case of two issues at once. I'm going to cut the plug wires back and redo them and poke around the ebox and associated wiring. I know the stators are a common failure point on these but I'm hoping its something more simple.

Crankshaft is out of the 550 engine and its about ready to go back in the cases. Still have to finish porting the cylinder, but it'll be quick work after that. Piston clearance was at 0.020" (!) which doesn't help anything. The spare cylinder measured at 0.010" which is still out of spec but better enough to let my girlfriends ride it. I'll get the removed cylinder bored out and get some pistons to match and should be good to go for a while. Crank bearings feel pretty good, fingers crossed.

Popped the steering cable on the 440, swapped that, what a pain. I also realized the pump in the 300 hull had a bored nozzle so I went and swapped that to the 440. Swamped my gps, but I'm pretty confident its doing an honest 40mph now. Super fun and nimble. I've been hitting a few boat wakes too. Nothing crazy but I think I got 6 feet of air when I caught a roughly 30 foot Bertram getting up on plane. Mad fun. Just like motocross except far fewer broken bones, I hope.

Fun times, lots of wrenching which isn't surprising but I'll be glad when I get these reliable and just needing maintenance instead of constantly chasing neglect. Really excited to get the 750 going.

 

[fastgtfairlane]

Those carbs are not easy to tune. I ran them for a season or two when I built my conversion ski several years ago. I can recall going up on the pilot and middle jets 1 or 2 sizes. I did lower popoff a little as well and removed 2 of the 3 screens as well as the rubber grommets on the air box. I want to say popoff was in rhe5mid 20s but I can't completely remember. I had a Westcoast 650 pipe that I cut the ribs off and extended 3 inches. It had a skat 20/22 impeller with a 68 or 69mm bored nozzle.