Thread: Back at it! 1996 SLT 780
06-23-2010, 12:06 AM #1
Back at it! 1996 SLT 780
Hey just like that when you don't think you're going to be tearing down engines anytime soon you're waist deep in a Polaris!
Okay so my friend Dave has a 1996 SLT 780. Dave and I grew up across the street from eachother and this is the craft that started it all for us. His family bought the 780 and a year later my Dad bought a 1996 SL900. So what started fourteen years ago when we were teenagers has turned in to a full blow obsession.
Anyways, this fourteen year old beast is now in need of some TLC! The ski had been ran year in and year out and well maintained up until just a few years ago, when it began a long slumber. Basically the ski had been sitting for about three or four years until just this season. Dave took the ski to where they bought it from and they replaced the battery, drained the fuel tank and apparently said it was "good to go". The ski had 196 hours on it before the slumber.
Now of course we all know that on a ski that has sat that long there are many things that should be done. Unfortunately that did not happen and I was unable to convince Dave to do otherwise before running the ski.
Well sure enough last Friday he was out on the River and it began killing on him randomly and then he started to notice power losses. First he could only get it up to 35 mph, then 25 mph, then finally 7 mph was all the faster it would go.
I told Dave to bring the ski up to my house and we would have a look!
He said there was a loud rattling happening so I wondered initially if it might be the shaft stub going or maybe it had failed, but upon seeing the ski there were no issues with the driveline, so I immediately just said "well, I might as well just do a compression test"
So out came the compression gauge and I was really happy when I saw a solid 120 plus on the MAG cylinder. Center was the same, 120 plus, no problem.
PTO unfortunately was not as lucky. After checking and rechecking the compression on that one several times (and looking at the spark plug) I knew it was time to pull off some cylinder heads.
Sure enough the PTO piston had a nice hole in it.
So our goal tonight was to get the cylinder and piston removed, assess the damage and make a plan of attack.
I examined the PTO carb and did find some rust particles and other debris in there (which certainly could cause a clog I suppose) but there were no obvious defects, nor did the fuel lines appear to be split or kinked in any manner.
My initial plan:
-Rebuild all three carbs
-New fuel tubing boat wide
I plan to go through the ski tomorrow and check support systems and other areas that might have caused the problem
Now if everyone else could just make some suggestions or offer any ideas or things to check I think we can do a nice restore on this ski.
06-23-2010, 05:50 AM #2
I have one that has been sitting for about the same time, maybe longer and I did all the maintenance and I still pull the plugs every time I run it because I am afraid that it is going to happen to me.
I rebuilt the carbs even though they didn't seem to need it. Surprisingly they were clean and the needles seemed to be seating fine but I rebuilt them anyway after reading the horror stories on here.
I put this in the tank also to try and make sure that the carbs stay clean. I don't know if it helps but my brother says that it does and he has a lot more experience than I do.
06-23-2010, 01:09 PM #3
- Join Date
- Jul 2007
- near Toronto, Canada
Nothing wrong with using Sta-Bil in the fuel. It will NOT clean out existing gunk or fix problems problems but it will reduce the rate that the fuel degrades while sitting if it is added when the fuel is still fresh.
That carb with rust particles, make really sure all the tiny internal passages are blown out with carb cleaner and actually flow properly.
06-23-2010, 02:19 PM #4
BTW: I thought the same thing about the Sta-Bil but my brother insists it will keep the carbs clean. That is why I made sure I posted that it was his comment and not mine. The guy knows everything when it comes to a car, but he just doesn't get the stupid stuff with these 2 strokes. He needs to listen and not treat everything like it's a freaking Audi.
06-23-2010, 03:20 PM #5
Without Stabil you run the risk of sucking a bunch of water through your carbs. If that's allowed to set in there it leads to rust and the formation of gelatanous goo. Once all the fuel evaporates away, the goo dries out and forms crystals that clog jets and passages. So, when you start up that ski that has set for years, the fuel can't dissolve the goo and/or crystals and results in running one or more cylinders lean and BOOM, there goes a piston.
Stabil also contains compounds that soften rubber to counteract the hardening effect ethanol has on rubber compounds. Basically the two reacting with the rubber keeps it right in the middle.
06-23-2010, 06:05 PM #6
Indeed...I am going to go through each carb and give them a thorough cleaning/revamp.
Now, I also removed the fuel pump today before I sent him home. I have never dealt with this infamous triple outlet pump I hear so much about. Is this something I can get a rebuild kit for? I am going to take the thing apart just to make sure its not all screwy either.
06-23-2010, 06:22 PM #7
Probably one of these 3 things main seal leaking, crank out of index, Fuel issues. You need to know what caused the piston to hole like that before you start w/ piston & rings if you just replace piston & rings youll just hole another piston. Lots of helpful people on this board.
06-24-2010, 12:55 AM #8
The screws on the intake manifold were pretty loose. I wonder if they could have been causing a leak.
The thing is this boat isn't mine and my buddy absolutely cannot do this without me.
So sure, I know the right thing to do is just tear down the engine and do a complete top end rebuild, and probably rebuild the crank and put in new seals too, but frankly, I have to balance being able to help him with this and not give away all my time for free. Plus, I don't know how much his family is willing to spend to get it right in terms of parts.
I think we are going to order rings, a piston, cylinder and carb kits, then when he brings it up here again, Ill do a leakdown test and check the index.
06-24-2010, 09:27 AM #9
Ket words being, how much are they willing to spend ? These projects can get costly, once you start rebuiling your going to find more problems that need hundred dollar bills thrown at it. Yes the intake leaking is no good. tighten that , . then index & leak down. Really spend some time & attention to the fuel delivery system.
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