650sx standup engine conversion

[mcraig79]

I have a 1990 650sx stand up and was wondering will a 750sx engine fit in there? what all has to come out for it to work? I would assume i have to of course change the pipe and electrical box..what about motor mounts and waterbox.

[Antwon]

Re: 650sx standup engine conversion

I don't think it would be worth the expense unless you have a 750 laying around. You could use your 650 electronics on the 750 engine but you would need to have the 750 case machined for the 650 stator.

[an_engnr]

Re: 650sx standup engine conversion

I just got a used 650 (judging from the VIN on the hull); the valve cover clearly says 750; does this indicate that the engine is a 750?

Thanks, and sorry if this is a stupid question.

-DS

[Antwon]

Re: 650sx standup engine conversion

It's a good question. Can you post a picture of the engine? It could be a 750. BONUS for you if it is.

[an_engnr]

Re: 650sx standup engine conversion

Here are two shots of the ski/engine...

[an_engnr]

Re: 650sx standup engine conversion

I've actually got it running, but it seems to 'run wild' when I start it... What are the common causes? Air leaks, etc?

Thanks!

-DS

[K6jet]

Re: 650sx standup engine conversion

what do you mean by run wild? It revs up to 5 grand RPM's at idle throttle? You need to be more specific.

[an_engnr]

Re: 650sx standup engine conversion

it was running wide open at which point I would cut it off...

after a little bit, it did start idling... particularly when I had the cover on.... do these things need to have the covers in place to run properly?

I'm doing this on my patio, and don't want to run it to long in case water is used for cooling (though I don't see any indication of this)... do these need to be in the water to run, or can I run it on my patio with impunity?

Once it started idling, (yeah!), it wouldn't respond well to throttle... it would work a little if I feathered it, but wouldn't hold a higher rpm. So, I took the carbs off, pulled the needle valves out, blew out the jets and cleaned the various bits with carb cleaner and put the mess back together; now it seems to idle well, but won't rev up at all with the throttle (I can rev it up by pushing gas in with the choke).

I really don't know what I'm doing here, so any help is appreciated :)

Thanks,

-DS

[K6jet]

Re: 650sx standup engine conversion

o geez, you started it up without water running through it?

How long did you have it running? (longest period of time)

Jetski's DO use water for cooling, it goes throughout the cylinders and jackets the exhaust.

Its fine if you have it started just to check it for 30 or so seconds (no longer), but having it running for longer then 30 seconds, ESPECIALLY at full throttle will damage the rubber parts in the coolant system, and can overheat your engine, and seize it, or blow a head gasket.

Most jetski's of that age did not come stock with whats called a flush kit. In other words, a tube under the hood that allows you to hook up your hose, and run freshwater backwards through the coolant system, in order to run it on land, and also, so you can flush sand, seaweed, or other debris out of your coolant system that eventually get stuck in there.

Jetski's are raw water cooled, so you need to flush it out ever use, or ever other use if your in freshwater (brackish Im assuming, so every use is good karma).

Things to know about starting on land-never run it for more then 5-6 minutes even WITH water hooked up to the ski, as the bearings in the pump (that ski is ALWAYS in forward, so the impellar always spins) arent submerged, so they can burn out, if you run it for prolonged periods on land.

Jetski's can run fine with the hood off or on, but pertaining to your symptoms with the hood on, rev with choke, it could be an airleak, or a carburation problem, or stale fuel, or a combination. I suggest you rebuild the carbs, and check the internal filter, as it may be clogged.

Also, for your knowledge, when running on land, since there is no resistance on the pump, it should idle at over 2 grand. Check for a tube under the hood that either has a cap on it that is unscrewed to hook a hose to, or has a weird one-way check valve that looks like something clips onto it. Flush kits as they are called vary in design, but if theres one, it should be easily accesible, and lead into the coolant system somewhere.

General knowledge:
NEVER run the hose without the ski's engine running (turn engine on, then within 15 seconds, turn on the water)! Coolant systems are designed, that if its running without the engine, you'll flooded your cylinders with water, and you can ruin your engine if you dont know what to do after that happens.

ALWAYS, stop the water before shutting the engine off, then rev the engine to 3/4 throttle in burst for 20 seconds to remove any remaining water from the coolant system (this goes for anytime you use the ski, if you cant flush it afterwards)


By the way, if the gas is old, remove it from the tank, and fill it with fresh gas. Gas will varnish and clog your carb if left for a while without stablizer.

[an_engnr]

Re: 650sx standup engine conversion

Thanks for all the information! I really appreciate it...

The next problem: I put the ski in the water this morning; cranked it up, and it started running... next thing I know it is sinking and the bilge pump quit. Needless to say, I dragged it back out in a hurry.

I was able to determine that water was entering the body of the jetski near the nose, and after removing the main exhaust thingy, pulling of the carbs, and taking out the gast tank, I found the cause... there was a big crack in a rubber piece of the exhaust; water was coming in through the tailpipe (on the side up front), and flooding into the main chamber through the crack in this rubber piece.

The Solution: replace the rubber piece.

The problem: I don't know where/how to get a replacement for this particular piece.

When I got up to the nose, I found that the muffler that was in place is a Supertrapp muffler which has a 1.75" inlet and a 5" outlet. The rubber piece that I need is a 90º elbow that goes from 5" back down to 1.75". Not seeing any mufflers on the supertrapp website, I am guessing that these aren't made anymore. So, the question: Where can I find a 90º rubber elbow that goes from 5" to 1.75" and is suitable for a wet exhaust?

OR: can I just replace the whole exhaust/elbow with a pice of tube... essentially do-away with the supertrapp muffler completely which means I could go 1.75" to 1.75" (easy to find)... would this be ridiculously loud? Does the supertrapp cone-shaped muffler have any type of keep-water-out function? Basically, would this be a reasonable course of action?

Thanks (again) in advance :)

-DS

[K6jet]

Re: 650sx standup engine conversion

just so you know, unless an aftermarket bilge pump was installed, the bilge pump is not electric, it runs on a venturi effect, its just a tube from the pump connected to a plastic box with holes in the bottom of the ski, so as long as the ski is running, its always sucking. Also, an exhaust leak may be causing the engines problems with starting, as 2-strokes depend on exhaust. Also, for ANY replacement parts, for new OEM, check www.rivamotorsports.com (their OEM parts finder) give them the year, brand, type, and they have full diagrams and pricing for every part but the hull. Also, OEM rips you off for new, so I always check salvage yards first, theres a list of all the big ones in the tech articles forum, call a few of them, up, 99 percent of the time somebody will have the part you need in great condition, and for half or less of the new price.

[dsolie]

Re: 650sx standup engine conversion

I have blown that same hose on my 550 and my brothers 650. Take it off and go to your local autoparts store. Size up the nearest universal radiator hose and there ya go. You might need to trim a little, but it's easy and like $10.

[joyenter]

Re: 650sx standup engine conversion

dsolie, it is not a regular hose he need, it is the blue hose in the picture.
Replace it with a water box there is some brands on the market and check out ebay and/or othere online auctions

[Antwon]

Re: 650sx standup engine conversion

DS- Looking at your pictures you have a 750 engine with a Westcoast pipe and exhaust manifold. Your running a 650 stator and front cover, your 750 cases have been machined for these mods.
It also sounds like you have had a closed throttle run away which usually an indication of some sort of air leak.You could test this out by doing a compression test on the top end and a pressure test on the bottom end.
If you can't find the parts for you supertrapp, just get an oem or aftermarket waterbox. Try some of the salvage yards for that supertrapp. Good luck.

[an_engnr]

Re: 650sx standup engine conversion

I replaced it with a loop of exhaust pipe (essentially doing away with the supertrapp muffler and corresponding rubber reducing elbow). Is there any problem (aside from increased noise) with running like this?

Thanks,

-DS