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  1. #1
    Derwood98's Avatar
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    2000 Polaris Pro 785 - Warning: Long Post

    Greetings,

    I am a new Polaris owner and was hoping (from the knowledge base I have been reading from), that maybe some of you could help me out.

    I recently purchased (what I thought was a 2001) Polaris Pro 785 from a private party. Visually, it looked to be in good condition and it sounded good on land (first mistake). He told me the MFD had a short in the wiring, but the display worked (second mistake). I paid $3,000 with trailer. Trailer is in really good shape. I called a Polaris dealer and had them run the VIN number later to find out it's a 2000. Even the registration says 2001. Humm. Guess I should have done a little more research.

    I took it to the lake and it didn't hardly go at all. It seemed like at WOT it was only getting to about 1/3 speed then it would tear out and then go slow again. Thinking the plugs were fouled, I pulled the machine into the garage to do some basic checks. I pulled the plugs, they looked good. I pulled the adjusting screws (noting the rotations outward) and blasted them out with carb cleaner. One thing to note, the primaries were adjusted out 1-1/2 turns the the secondaries were completely closed. Everything appeared to be okay so we put it back in the water to try and make some carb adjustments with no success. Since I didn't have a service manual, I had no idea where they should be set up, but I knew the secondaries should not be closed. Bummed, I drove it home.

    I first checked the compression. Front cylinder (toward hull) 90 PSIG, center and rear at 130. Again with no book, didn't know what they should be, but I knew I had a problem. I checked the MFD to see if I could find the short, only to find the harness all hacked up and the wires were pushed on with solderless terminals and were shorted out. Next, I pulled the exhaust valves to find they had not been cleaned in years and had not operated in a long time as they were loaded with carbon and no signs of movement. I pulled those out and got them all cleaned up to like new condition. Next was the exhaust valve servo. Opened that up and come to find it was full of water and everything was rusted shut. I was able to take it apart and get everything all in working order, but since I don't have a book, I am not sure how to test it. (BTW, I should have a book mid next week which will make life a lot easier).

    Since I was this far, I decided to do an entire strip down and rebuild this thing from the ground up. I have everything pulled except for the engine which is coming out this weekend. I also found out the temp sensor in the head was stripped out and held in with silicone. Looks like I will be replacing the head along with the temp sensor. The good news is that the cylinder walls look to be in great shape and the top of the pistons look good too. I guess I will find out more when I pull the motor.

    I purchased a new MFD harness from the dealer and guess what, it's a 12 pin harness and the MFD that's on the machine is an 8 pin. To make matters worse, it's not even the correct MFD for the machine. Anyone know where I can find the correct one?

    Thanks for staying with me thus far. So, here is what I am looking to do. I would like to get the machine back to at least factory specifications and if I can do a little bolt on performance upgrades while I am at, I am all for it.

    I have done some searching and saw a few pretty cool builds on here and was hoping maybe you could share some of your tips and tricks. Also, good sources for parts, tuning, etc would be greatly appreciated. The good news is that I am really good with the tools, just not much experience with PWC's and two cycle engines.

    Thank you,

    Darrin


  2. #2
    bowsniper's Avatar
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    Warning! Long Post! lol


    Well first off. WELCOME to the Hulk! You'll find all you need to get your ski running from these guys. they are the best in the world on polaris's and about 52 members here have 785 Pros!.

    I have a 2000 Pro785 like yourself. I'm in the process of changing my stator. you can buy a 8 pin to a 12 convertor for the wiring harness..

    BTW.. It's called a HIN not a VIN Hin stands for Hull Idenification number! Just wanted to let ya know..

    I would first get your eggs in 1 basket with that wrong registration.. the water police wouldn't like that! They could impound it.



    when the lower screws are in all the way, you are still getting gas! usually they are 1/2 turn out.. but some skis have different carb setups and not all will be indentical. so be aware of that many of these skis are modified and 1 way for one person may not work in your situation. so always ask lots of questions and be certain of what your doing first..

    90 psi means you have a problem to fix.. Either just rings or maybe a new piston, depends whats wrong exactly.. they should only be 5% or absolute max would be 10% between cylinders. So yeah, your way off on that cylinder..

    The stripped fitting can be repaired with a die and tap and a hela-coil, no biggie there. even if you have to go big, you can still get a reducer for it.

    1.5 out on the highs is a good starting point. if there are caps on the top screws, take them off to expose the brass screw if so equipped. The lower screws are your lows and have tees on them. of course the idle screw is on the carb throttle rail at the end with a screw and spring around the screw, set that to 1250 rpms or so. just putzing along with no wake but still idling nicely.. do that after your set up your carbs..

    Next would be to ask... how long has it been since the fuel system been cleaned or rebuilt. these skis in general hate dirty carbs and weak diaphrams. I would also consider changing all the fuel lines too. every one of them! use 1/4 inch clear blue or us coast guard gas line. some like the colored type for bling factor!

    I would rebuild both fuel pumps and do all the carbs..\

    Sorry to hear your valve motor is rusty... makes me think the ski was sunk at one time.. usually they look brand new when opened up. theres a procedure for testing the valve moter for operation if you need that..


    when you said the pistons look good. what do they look like? are they clean? black? half and half? or little clean marks on them? post a picture if you can or video.. that will help us help you better!. we can show ya how to post pics if necessary.

    All the parts you need are here somewhere as well as great advice from the best techs,machinists,fabricators,speed demons, racers,mechanics and electrical genius's(k-447!. Just ask and someone will chime in to help you out..

  3. #3
    ujustlost's Avatar
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    Hello, the carbs were about what they should be. The lows are 1 turn out and the highs are supposed to be closed. The ski originally came with a 12 pin mfd and harness, so the dealership sold you the right harness. It was not uncommon to change the mfd's to a 8 pin after the original 12 pin went bad.

    As far as the registration goes, I wouldn't worry about it. My brother bought a brand new car in 2002 and it was vin'd a 2001 but the registration was given as 2002 because it was over stock from the year before and was still brand new. Sense the pro's last year was 2000, they probable just did the same thing when the origional owner bought it sometime after 2000.

    As mentioned above replace all fuel and oil lines and rebuild the carbs and install new needles and seats.

  4. #4
    Derwood98's Avatar
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    Thanks guys for the warm welcome and the suggestions. Here is what I know so far. I already mentioned the exhaust valves and servo, please see the attached pictures. I pulled the motor and lifted the cylinders to find another suprise. Cylinder #1 was scored and the piston scored, same thing on # 2 and on # 3. WTF??? Boy did I get screwed. Looks like the cylinders were honed to smooth over the marks and put back together for a quick sale.








    So, now the question is, can the cylinders be bored out and put in oversized pistons? And/or where do I get such items and who can do the work? Now, I think it would be a good idea to tear into the rotating assembly to see what the crank lools like. What a bummer. This will be a little easier once my book finally arrives.

    Looks like this thread is going to be a question and answer along with a rebuild thread. Thank you in advance for your support.

    Here are some shots from the inside of the boat. It's in fairly good shape. At least something is...






  5. #5
    ujustlost's Avatar
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    The pistons look a little scored but the jug doesnt look all that bad. Try taking some acid and clean the jug up, it might just be some aluminum from the pistons that make it look scored. The jugs are nikasiled and it is a lot harder than the aluminum pistons. Assuming the crank is good, Get yourself a set of standard size 750 pistons,rings,pins and clips and depending on how bad your jugs are either put it back together or send all the pistons and jugs out to get re niked. To answer your question, yes it is possible to get the jugs bored out and sleeved for oversized pistons but I personally wouldn't do it. The outside of the ski looks to be in good condition.

  6. #6
    bowsniper's Avatar
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    see all those grey fuel lines? they have to go. they develop goop in them and wreck your carbs.. your wash on the pistons looked good actually.. i wonder why they are scuffed up so bad if the wash was that good.? makes me wonder..

    bigger pistons is not the way to go(if you want to save money!).. you should have the cylinders replated and go with stock pistons. that ski is set up as a race ski and the bore stroke combo works perfect for acceleration and torque. plus the port timing gets thrown off and you need to have the cylinder port matched, which is more money..
    if you bore, you may need to get it sleeved too.. more money. just trying to keep costs down 4 ya.

    these cylinders are nikisil plated.. thats a nickel alloy which is super strong and transfers heat well. plus the friction factor is less with that coating. its pretty thin.a few thousands thick. its pretty pricey to have the cylinder re-nikisil'd. Just depends on what your looking to do.. the replating brings old jugs back into spec. that way you can use stock pistons again.

    sharps marine does work on these motors. i would take the crank cases apart and inspect the crank too. your already this far into it.. if its at all rusty, its hit. it will blow up within hours of riding it. if everything spins smoothly and feels good, then your ok..

    your controller box is all rusty i see. does it work? maybe a good blow off with wd-40 might clean it up pretty good. if the crank is rusty, i would suspect a swamping of the ski at some point in the past. that would explain why the controller box is so rusty and possibly the stator up front too. let us know what the stator looks like if ya could.. if it is.....your ski was swamped. it happened to another members ski on here. hyoctane23's.

    yeah 3 g's would of been ok.. if it ran perfect.. ugh! the guys here always say to do a compression check first before anything else.. then you know it turns over, the battery is good and if it fires up, and what the compression numbers are. you would of seen the 90 early on and had your say about things. i know,,, hindsight sucks,, but a lesson learned. its a great ski by the way. I love mine..

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    Contact Sharp's Marine or Randy from Watcon.com

    They can set you up with what you need.

  8. #8

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    You do not want to bore or sleeve your cylinders!!!!!!!!!!!!!!! if you need them replated go to Power Seal in Pa. and for all your parts go to Partspit.com or babbittsonline.com these are your BEST parts resources

    And for any crankshaft work you need go to Crankworks or my favorite is Jeff at Midwest crankshaft in Greenbay WI. either of these are your best choices !!!!!!!!!!!

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome

    You should click the links below

  10. #10
    Derwood98's Avatar
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    Quote Originally Posted by ujustlost View Post
    The pistons look a little scored but the jug doesnt look all that bad. Try taking some acid and clean the jug up, it might just be some aluminum from the pistons that make it look scored. The jugs are nikasiled and it is a lot harder than the aluminum pistons. Assuming the crank is good, Get yourself a set of standard size 750 pistons,rings,pins and clips and depending on how bad your jugs are either put it back together or send all the pistons and jugs out to get re niked. To answer your question, yes it is possible to get the jugs bored out and sleeved for oversized pistons but I personally wouldn't do it. The outside of the ski looks to be in good condition.
    Upon further inspection, it does look like piston residue on the cylinder walls. Looks like someone tried to hone it out. What type of acid would a person use to remove it or would I be better off just sending them somewhere to get re nikasiled and back to factory specs? I will get a better look at the crank once I finish making a flywheel puller, unless someone has one I can borrow.. Hint, Hint. Once I get into the bottom end I will have a better idea of what parts I am going to need.

    The next step is to strip and rebuild the carbs. Are there any kits availible with all the necessary parts, gaskets, diaphrams, springs, etc that I am going to need or do I have to order everything onesie twosie?

    I pulled the trim actuator and found it a pile of rust. At least the last person stuck a little grease on rusty gears to help free up the mess. It's all cleaned up, resealed and back on the boat. Works good too.

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