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  1. #1
    jcc011185's Avatar
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    Question Help me iron out some wrinkles in my 96 sl780.....

    Ok, this is a collaboration thread for my modified 96 sl780 jet ski. A summarizion of all my previous confusing and information lacking threads...

    As many of you already know, I have multiple inquries/problems/etc... scattered all around the board, and per the suggestion of another, I am going to round up all the information and we'll just forget about all my other threads and hopefully this one, with all the information out in the open, I can get my ski running like it should be with the mods it has.

    My ski:

    Year/Make/Model: 1996 Polaris Sl780
    Compression: 115 each cylinder
    Pre-mix: No, but my pump is working fine and that is verified
    Gasoline: 93 octane premium always no additives (North Carolina)
    Ride places: so far, only freshwater lakes, that are calm and rough water.

    Preamble: I got the ski off of ebay in good shape... the MFD was not working, but a that of course turned out to be just the fuse in the electrical box. Then, after replacing the fuse and getting the MFD working, the ski went into limp mode, creating my first set of emergency threads and I thought I had hydrolocked the ski etc... Turns out the gas float was bad and I replaced it with a new one, and limp mode was gone. I also forgot to plug the hull ONCE around the same time, leading me to belive that I had gotten some water in the engine, which wasn't the case. Per instructions by sealion, I tilted the ski all the way on the trailer and pulled the pulse line and ran the starter without the lanyard just to make sure but in only pumped gas out. Anyway, the verdict to that was that it was just limp mode, and nothing else I never actually got water in the engine to my knowledge, plus the water level when the ski flooded was just up to the electrical box, and no where close to the carbs where it could injest some water. A "little" water got in the electrical box, but it did not affect anything... I pulled the circuit board, the sauder circles weren't even rusted... The ski ran fine when out of limp mode...

    Then.. came the modifications:

    First, I got a pro 785 programmable CDI from ATSaaron through ebay. Thanks to the generous instructions supplied by ph2ocraft, swapping the CDI's out was a snap, and it has so far made the most noticeable difference to the ski, I loved it! A little sputtering at the low RPMS when just using it with the stock ski.

    Next, I got the skat trak 12/17 impeller... Got it off of ebay (http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=009) It is not an aftermarket, but a stock 12/17. At the same time, I got also off of ebay an ocean pro 3" extended ride plate, and a watercross dual scoop design intake grate. (http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=019) I swapped out the impeller as well as the ride plate and grate at the same time. When I took the ski out the first time I could tell instantly it was severly lagging, didn't run much at all that day getting just over 6000 rpms max, and speeds in the upper 30's to lower 40's (I was getting 50's easily with the stock setup and also after adding the pro cdi)

    Shortly after that, I got my 93 sl650 drypipe also off of ebay (http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=016) I installed it (A PAIN!) and took the ski out the next day... the exhaust sounded different, but the ski did not act different.. I set the carbs to the 96 slx780 specs and I could get max 6200 rpms and lower 40's mph (though I did not run much and only short bursts) I was stumped, so after I got home I posted the results... sealion recommended I remove my pump cone spacer which I did, and bore the nozzle to 87mm from 84mm which I did, and to also remove the watercross intake grate and put my stock one back on for now, as that grate was too aggressive for my ski, which I did, and finally to turn out all my carb adjustment screws (high and low) 2 and 1/2 turns from seated which I did as well (all the way out)... I took it out today after that and did not notice a difference. 6200 rpm and less, mid 40's max and it was slow getting out of the hole. So, I adjusted the lows to the best of my ability (to where I thought I had the smoothest idle) and set my idle adjustment screw to around 1300rpms. I started to turn in the highs and I gradually got it up to 6440rpms which was the max that I was getting before even starting the mods...

    Lastly, I noticed that with my ocean pro ride plate, the trim adjustment function is useless as it only performs well when it is in the middle.. if I adjust the trim up, it rides poor and slow, and the front end no longer raises like it used to (before the OP ride plate). If I put the trim down, well it acts still like it should, lowering the front end of the boat, thus also slowing the ski down. I find the best position is right in the middle... is this normal, and is the OP ride plate hurting my performance OR top speed in any way?

    I'm working on getting an extended pump setup together from either zigler, ebay, or a local PWC guy with several parting out SLX's... Also the same local guy says he can re-jet my carbs and adjust them to where they should be for my setup (he's familiar with these mods) but it will cost me only $100 and I am perfectly willing to spend the money once I'm re-assured that this is my problem with my current setup...

    NOW, I'm just trying to figure out why I'm not getting the 6900 - 7000 rpms and in the upper 50's mph that sealion got on his 780 with these mods... I realize he has 44mm carbs, but it seemed that when I leaned out the high speed screws, it got better and when they were richer, it was way worse...? Your thoughts?
    Whew, I think that pretty much summerizes everything performance wise I have done to the ski (to the best of my knowledge as of now)... and my end result: I'm back where I started !

    What do I do now.....?

    Jared
    Last edited by jcc011185; 10-29-2006 at 01:58 AM.


  2. #2
    ph2ocraft's Avatar
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    The very first thing I would do is verify the crankshaft is not out of index. Until you know the crank is O.K. you're chasing your tail.
    Now let's say your crank is indexed properly and you have no issues with a rod not being bent or a section of the crank has been "twisted" what can it be?

    Carbs wayyy out of calibration
    Pitch of the impeller toooooo tall
    Worn or damaged impeller/stator etc.

    The easiest way is to put things back the way they were and get some base numbers. Leave the pipe but put the old plate and impeller back on the craft. I know you can't change the bored nozzle, so you'll need to leave that as is for now.

    First add some race fuel 50/50 mix
    Return the jetting/adjustments back to stock. Take small 100 yard bursts and see what your RPM readings are.
    Report back.
    We want to know;
    How is the crank index?
    Compression again?
    Plug reading?
    Max RPM's
    Is the accelerator cable fully opening the carb flaps?
    I'm sure others will have some more information and questions.

  3. #3
    ph2ocraft's Avatar
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    Or you can leave things as they are and borrow an impeller from somebody else and see what you get?

  4. #4
    BigDaddyPT's Avatar
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    I am no expert (obviously) by my posts but it sounds like your problems started with the impeller changing. I'm good with boats and boat propellers however. To me, it sounds like you have the wrong impeller in there. I could be wrong but try switching it back and see what happens.

    just trying to help since everyone's been so nice to me!

  5. #5
    jcc011185's Avatar
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    Ok, crankshaft out of index... what does it mean and how do I check? I can tell you, that when I pulled the shaft to replace the impeller, it seemed almost brand new, now show of any grind ever, all the "teeth" were in great shape... so was the impeller's teeth...

    Also, as a novice, I do not know what all this means: "Now let's say your crank is indexed properly and you have no issues with a rod not being bent or a section of the crank has been "twisted" what can it be?"

    The rod definatly did not look bent.

    How should I go about doing this, just return it to the way it was (take off the OP plate, and put the stocker back on, and also put the stock impeller on... what about the pump cone spacer... I didn't notice a difference with it on or off...

    Then, take some numbers and report back to you guys. Then, how should I go about putting the mods back on, I assume one at a time and see the result it yeilds? I feel it has something to do with the impeller, and probably the carbs being too far off for my setup.. but at the time they were stock jetted and set to the 96 slx780 specs (not sl780, the slightly higher slx780)

    There is no gas station around here that sells race fuel.. and I definatly do not want to have to convert to using that, or anything else that I cannot get at most gas stations...

    Oh, the accelerator cable fully opens the carbs.. they sit perfectly vertical when you open the throttle fully, and perfectly horizontal when you let off the throttle... see I can answer at least one thing

    Oh, and of course, out of the water it has no problem instantly reaching the rev limiter of the pro 785 CDI (I know, only for a second or two) But just to verify, the RPMS are possible and it's not something electrical etc...

    Jared

  6. #6
    jcc011185's Avatar
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    BigdaddyPT, EXACTLY my thoughts... As sealion suggested on another thread, this might just be a re-pitched impeller and not actually be what it was stock...afterall, it came from a much more powerful machine, that might have required a different pitch for it's mods, go figure...

    Guys, what am I to expect when putting the stock impeller on... do I really "need" the so called 12/17? Just curious, cuz if it's the problem, I've got to start looking for another one and I do not see any listed...

    Jared

  7. #7
    ph2ocraft's Avatar
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    O.K. with no race fuel (that was just so you didn't burn anything down while testing) let's go to swapping the impeller as BD has suggested and see what RPM's you get.
    I'm pretty sure if you talk with Randy from Watcon and buy an impeller from him, he'll give you a few to try. I'm sure he'll have some suggestions for impeller pitch, it's a start.
    Maybe check with the guys and see who has an impeller they might be able to loan for testing purposes.

  8. #8
    jcc011185's Avatar
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    Ph2ocraft... good idea! what pitch should I want to borrow? anybody have one that they would let me borrow? (I cover shipping both ways of course...)... that sounds perfectly logical, since I only have this one which I am unsure of it's "real" pitch, and my stocker (polaris 5131079 progressive 4 blade) to test with...

  9. #9
    BigDaddyPT's Avatar
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    I'd suggest starting out with the stock pitch impeller for that machine and see how you like it or maybe a slightly higher pitch.

  10. #10
    SeaLion's Avatar
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    The pic shows an impeller that says 15-20 written on it. Maybe it was repitched to a 15-20 which would definitely mean too much pitch and probably close to 6200 max rpm. Even though the part number matches a stock 12/17, people repitch impellers all the time. The new pitch should have been etched into the inside of the hub though. Most, if not all impeller repitch places do this to minimize confusion. There are guys that try to bend their own impellers too. This is what sucks about buying used. Maybe the pwc shop you know has a pitch gauge and can measure the actual pitch of the impeller. You could try the old impeller again. If rpms go up, that means you didn't get a 12/17? Good news is that you can have it repitched to a 12/17.

    BigDaddy, This set up requires a lower pitch impeller than stock to work properly.

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