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Thread: 2000 785 Pro

  1. #1

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    2000 785 Pro

    Hi all,

    Now that there is snow in the forecast I picked up a PWC last weekend (was not really the plan). it's a 2000 785 Pro. I've wanted a 785 Pro for a very long time. Looks as new, runs, well, not so great. All stock except for new Wiseco pistons and and a new cylinder. When I first looked at it a couple of months ago, it ran poorly, compression was 115, 110, 90 so I passed on the sale. The owner said it needed nothing, but it obviously did, so he put a new cylinder and pistons in it. Compression is now 121, 121, 124, but it runs even worse now. It struggles to stay idling (would idle fine before), and labors very hard just to get on plane. Trim is stuck on "up" position even though the MFD shows that it is going up and down. No flashing lights- as in limp home mode- that I recall. I tried new plugs, but it didn't matter. It will rev fine out of the water, but struggles to run in the water. The "pissers" emit water when running. I even thought I saw 5000 rpm on the MFD (although it sounded more like 3000 rpm), but it didn't go over 20 mph, although I got it to go 38 mph before the top end rebuild. Revving on the trailer, I could see some power valve movement. I am trying to contact the mechanic to see if he cleaned the carbs as well as doing the top end. I will pull the reeds and check them after the carbs get checked, if the carbs haven't been already done. Any other suggestions/guidance would be appreciated. I think I have read every 785 Pro post on this web site, so I got a start... Tony

  2. #2
    Moderator HiPeRcO's Avatar
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    Welcome to GH, and congrats on your purchase. You picked a classic to get started with, not for the faint of heart from a repair and maintenance standpoint from what I understand I'm sure some 785 gurus will be by shortly to offer assistance.

  3. #3

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    Thanks HiPeRcO,

    It isn't my first PWC, but they have all been Polaris; I bought a 1995 SLX in 2000 and recently sold it. It was a fun boat. I also had a 1996 SLX for a short time, but it was all stock, and didn't handle as well, so I sold it. I bought a 1996 SL 700 (no sponsons, flat bottom) and still have it. It is very different than the SLX in terms of handling. I like the aggressive handling better; that's why I wanted a Pro.

  4. #4
    rpa101's Avatar
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    Quote Originally Posted by tpssonic View Post
    Hi all,

    Now that there is snow in the forecast I picked up a PWC last weekend (was not really the plan). it's a 2000 785 Pro. I've wanted a 785 Pro for a very long time. Looks as new, runs, well, not so great. All stock except for new Wiseco pistons and and a new cylinder. When I first looked at it a couple of months ago, it ran poorly, compression was 115, 110, 90 so I passed on the sale. The owner said it needed nothing, but it obviously did, so he put a new cylinder and pistons in it. Compression is now 121, 121, 124, but it runs even worse now. It struggles to stay idling (would idle fine before), and labors very hard just to get on plane. Trim is stuck on "up" position even though the MFD shows that it is going up and down. No flashing lights- as in limp home mode- that I recall. I tried new plugs, but it didn't matter. It will rev fine out of the water, but struggles to run in the water. The "pissers" emit water when running. I even thought I saw 5000 rpm on the MFD (although it sounded more like 3000 rpm), but it didn't go over 20 mph, although I got it to go 38 mph before the top end rebuild. Revving on the trailer, I could see some power valve movement. I am trying to contact the mechanic to see if he cleaned the carbs as well as doing the top end. I will pull the reeds and check them after the carbs get checked, if the carbs haven't been already done. Any other suggestions/guidance would be appreciated. I think I have read every 785 Pro post on this web site, so I got a start... Tony
    Don’t take anything for granted ! Go through everything your self , forget the mechanic go through the carbs your self , check the e box for water intrusion, pressure check the pipes , replace all fuel lines if there original. If it was me doing this again I would pull the motor and go through everything checking stator flywheel, seals ,reeds ,carbs, if it has forged pistons make sure the clearance is correct?

  5. #5

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    Compression numbers seem low, should be 150 across the board. Start with the basics, exhaust valves, clean and adjust as per manual. A must is pressure test the pipes, 10 psi for 10 minutes. Rebuild the carbs with Mikuni kits. And last, check the stator, which sounds like it could be the issue. 785's are known for that.
    I have owned and race these boats, and the above are usally the prime reason for your issue. I would suggest pulling the head and checking piston ring to wall clearance too. And as apa101 stated, tearing down the motor and rebuilding is not a bad idea.


  6. #6

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    Thanks for the guidance. I will be doing those checks.

  7. #7

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    Wiseco forged pistons

    Quote Originally Posted by tpssonic View Post
    Thanks for the guidance. I will be doing those checks.
    Me too i'm going to build a pro 785 engine with wiseco forged pistons....

    All of you Pro785's guru have some tips at this regards....
    Clearence and any other suggestions

    Thanks

  8. #8

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    modesto, Since the Wisecos are forged pistons, they are more dense in construction and as a result tend to "grow" more when heated. That thermal expansion is taken into account during the manufacturing process of the slug and is not a problem when seeing safe air/fuel ratios. It is more of a concern when a cast iron-lined cylinder is bored and the forged piston-to-cylinder wall clearance is on the tight side of spec. It is more of an issue in the winter (read: snowmobile industry) when the combination of frigid temperatures and not-properly-atomized fuel. In the cold engine scenario, the engine sees the A/F mixture as a lean because a good part of the fuel is not properly atomized and can't burn properly when asked to run WOT immediately after start-up. The combination of cold cylinder walls and a hot and quickly "growing" piston from a too lean A/F mixture causes the dreaded seizure. Properly warm up your PWC engine before doing WOT blasts. Their quickly expanding rate is why forged pistons (e.g. Wisecos) got a bad reputation, and were referred to as "Seizecos" Since the Pro 785 cylinders are nicasiled, there is not a lot you can do about piston-to-cylinder wall clearance if you're just replacing the pistons; just ensure that ring gaps are sufficient. Check them all. That being said, the forged pistons are stronger and much more stable and forgiving in many conditions (especially in heavy deto conditions, like when timing is too advanced, too lean A/F ratio, and when using nitrous hehe, hehe, heh...). This is especially important on the pto end piston- at WOT conditions under load- where slight, but cumulative, crankshaft twist can act as increased timing in triple-cylinder engines.
    Last edited by tpssonic; 11-03-2017 at 08:47 AM. Reason: added a thought

  9. #9

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    Quote Originally Posted by tpssonic View Post
    modesto, Since the Wisecos are forged pistons, they are more dense in construction and as a result tend to "grow" more when heated. That thermal expansion is taken into account during the manufacturing process of the slug and is not a problem when seeing safe air/fuel ratios. It is more of a concern when a cast iron-lined cylinder is bored and the forged piston-to-cylinder wall clearance is on the tight side of spec. It is more of an issue in the winter (read: snowmobile industry) when the combination of frigid temperatures and not-properly-atomized fuel. In the cold engine scenario, the engine sees the A/F mixture as a lean because a good part of the fuel is not properly atomized and can't burn properly when asked to run WOT immediately after start-up. The combination of cold cylinder walls and a hot and quickly "growing" piston from a too lean A/F mixture causes the dreaded seizure. Properly warm up your PWC engine before doing WOT blasts. Their quickly expanding rate is why forged pistons (e.g. Wisecos) got a bad reputation, and were referred to as "Seizecos" Since the Pro 785 cylinders are nicasiled, there is not a lot you can do about piston-to-cylinder wall clearance if you're just replacing the pistons; just ensure that ring gaps are sufficient. Check them all. That being said, the forged pistons are stronger and much more stable and forgiving in many conditions (especially in heavy deto conditions, like when timing is too advanced, too lean A/F ratio, and when using nitrous hehe, hehe, heh...). This is especially important on the pto end piston- at WOT conditions under load- where slight, but cumulative, crankshaft twist can act as increased timing in triple-cylinder engines.

    Thanks for the quickly and detailed answer....

    Anyway due to the fact pistons are news ,honing the cyilinder should be a must....

    Really?

  10. #10

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    You will get better ring seal if you hone it. However, the stock cylinders have a proprietary and thin coating of nickel, carbon, and silicone on the interior cylinder walls (hence, the name nicasil, or nikasil, etc.) that offers better heat dissipation and resistance to scoring, but is very hard and not easily honed properly with the common hones used for cast iron liners. IIRC, the nicasil cylinders are honed with a diamond hone. You can make some passes with your berry and/or bar hone and it probably won't hurt, especially if there is any aluminum residue. Just knock the glaze off if you can and lay a light 60 degree cross-hatch. Ensure you wash the cylinders THOROUGHLY (i.e repeatedly) with warm soapy water and rinse very well before fitting the pistons.

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