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  1. #1
    Buck3yeRideR's Avatar
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    Cool Getting 2 - 650 std's on the water with UPDATES

    Picked up a couple 1995 SL 650 std's about a month ago for cheap. Installed fresh batteries and both worked for roughly 3 hours until ski#2 kept stalling.

    ski #1 - the better of the two skis, ran great for 3 hours but stalled every once in a while. Three weeks later (last weekend) I removed the thermostat and spring device next to it, trimmed plug wires, replaced plugs, changed grease fitting, checked all gas/oil lines, checked engine bolts, installed 780 F/A and attempted to adjust high carb setting. After i did all this the ski seemed to run almost perfect with minimal stalling, however if you go from idle to WOT the ski sometimes falls flat until i play with the throttle and then the RPMS will go up. Also did a compression check and numbers were mag115-120-115. I plan on doing the triple outlet pump upgrade, and maybe the carb rebuilds if i need it, what do you guys think? Anything else i should check?

    ski #2 - the worse of the two skis, ran good for 3 hours and kept up with ski #1, however at the end of those 3 hours it would keep stalling randomly. Is also hard to start. Three weeks later (last weekend) i did a compression test and numbers were mag15(bleeding off),115,110. I'm gonna say i burnt the piston up due to a lousy fuel pump since the mag is the last cylinder to be supplied fuel. Now i'll ask how hard is it to replace the piston and cylinder? Do i have to removed the engine from the ski? whats a good price estimate to buy good used ones? Just looking for pointers here on what to do. I was thinking about selling it as a whole but if i can fix it for a good price i might do it. Since even the other 2 cylinders do not have prime compression am i in for a total engine rebuild, or can i get away with just replacing the 1 piston/cylinder? I got these for free and am only planning to use them for 1 year or so, so minimal costs is where i am in terms of money.

    replies are appreciated.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Carb rebuilds are not optional on these older engines. The risk of engine damage is high without a proper fuel system refresh and carb rebuilding.

    Cylinder can be replaced with engine in the hull.

    Have a look through my signature links for more tips and info

  3. #3
    Buck3yeRideR's Avatar
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    Got out on the lake this weekend and had fun, but also had some more problems.

    First i'll start out with ski #1, the good ski, that is still currently running. I installed a 780 FA since the original was completely cracked and turned out the appropriate carb screw 1/2 turn and it ran great. Re- routed the oil injection lines/brass fittings to the top of the FA.



    However at some point the whole 780 FA fell off and starved the engine of oil. I have no idea how this happened as i tend to overtighten things. Anyways i was on the water and it stalled at WOT, started again and stalled at WOT, now at this time the battery would barely crank the engine over so i had to play with it til it did. Finally started up and i idled back to the docks where i found the FA fell off. Did a compression check and now my MAG cylinder went from 115psi last week to 100psi however it still runs, just harder to get started and keep going. Put oil in the cylinders, carbs, and put the FA on to get it lubed up as fast i could. Anyone know why it was hard to crank at that one time? Internal parts expanding too much from the heat? What would the most likely damage be, rings? Any i should ask why was it only stalling at WOT?




    Ski#2, the one not currently running.
    With MAG compression at 15 psi i pulled the head expecting a holed piston. However there was no such hole and all looked fine to me. Cylinder felt crosshatched and correct however maybe a tad rougher on 2 different sides. So since its not a holed piston what could be the causes; rings, reeds?




    I was VERY surprised to find the head gasket had only tiny variable sized holes for the water outlets. Do they all come like this? I thought maybe it was build up but looks to me like its gasket material. I may be taking all heads off my 2 skis and putting new head gaskets on now after seeing this.




    I also dropped my wrench under the gas tank and had a great experience taking it out. I noticed that opens up the hull a lot.

    And finally a pic for the suggested advice i've read on here. Thanks for your support guys and all responses!

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Moral of the story; When the engine suddenly dies unexpectedly, don't just restart it. Take the seat off and have a look-see

    Lack of oil will show up first on the cylinder walls. Excess friction causes accelerated wear and extra heat. Too much heat causes pistons to seize in the cylinder bores.

    You may have scored the cylinder walls. If you are lucky you may just need a light re-honing and new piston rings.

    Why did you relocate the oil feed from the factory location?

    Regarding the non-running engine, is the piston the correct size for the cylinder bore?

  5. #5
    Tow-in-Barrels's Avatar
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    just a piece of general mechanic advise, as you seem to be open to suggestion. If you tent to over tighten things you should buy a torque wrench, get multiple attachments to adapt all your sockets and even screw driver tips to it, and use it as per the manufacturers suggested torque specifications for each engine part. You can find the numbers for every nut and bolt in multiple places on this and other web sites and/or buy the polaris manual online.

    Friends don't let friends remain over tighteners. more is not better in this case. (nor any other engine case for that matter,, yuk yuk yuk.....)

  6. #6
    Buck3yeRideR's Avatar
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    Quote Originally Posted by K447 View Post
    Moral of the story; When the engine suddenly dies unexpectedly, don't just restart it. Take the seat off and have a look-see

    Lack of oil will show up first on the cylinder walls. Excess friction causes accelerated wear and extra heat. Too much heat causes pistons to seize in the cylinder bores.

    You may have scored the cylinder walls. If you are lucky you may just need a light re-honing and new piston rings.

    Why did you relocate the oil feed from the factory location?

    Regarding the non-running engine, is the piston the correct size for the cylinder bore?
    Yes i'm having lots of hard learned experiences it seems with these ski's. I guess now i know though. So would you suggest the lack of oil just harmed the MAG cylinder and not the other 2 since compression remains the same on them?

    I had to relocate the factory oil feed location when i installed the 780 FA. The 650 FA had holes for the pil fittings in the base plate, while the 780 FA did not. Took me a while to figure out where to put the injection fittings, then i noticed 3 plugs that were on top of the FA cover and thats where i put them. Is there another place? B/c i sure didn't see one.

    on ski#2 how do i tell if its the correct size piston? Honestly to me it looks like theres a small gap b/w the cylinder and piston.


    So in short terms. looks like i need to swap in 1 cylinder/piston/head on each ski.

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