First time starting 03 MC900 sled in over 3 years...

Nov 20, 2017
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As previously posted, I bought a 03 Mountain Cat 900 that had sit in a garage for the better part of 3.5 years without being run for $500... I've fixed a few things on it such as the steering nut being disconnected on the steering shaft from the actual steering rod, cleaned carb jets, replaced spark plugs, restrung pull start cord, etc but couldn't get it to actually turn over and start using choke and numerous pulls (with a bit of 2 cycle oil in each cylinder for safe measure). I have checked and all other fluids are good to go (oil, coolant, brake fluid, etc.)

Tonight, I decided to put a little bit of 2 cycle oil in each cylinder and spray a bit of starting fluid in each cylinder to see if she starts. First pull, started right up and of course, smoke was pouring out. I do know that after sitting 2 cycle engines can put out A LOT of smoke. I've read that more smoke is actually better because is shows that the oil is being injected.... it's when you don't see smoke at startup you should worry. I pulled it out onto the driveway and let it run for a minute or so and the smoke started to subside a bit. Also was able to test the mechanical reverse, which works perfectly. Actually I had a hard time not spinning the track on my angled driveway... this machine has a LOT of power! :)

With that said, I've never started up a sled that has sit for the better part of 3 years of not being run. Of course I know the gas is bad and I'm going to siphon as much out as I can and replace with fresh 91octane.

Beyond checking bearings, etc. what should I be aware of with running something like this? Should I just let her run for a few minutes and let the engine burn off carbon deposits, etc or should I not try to start again without checking something?

Any advice is appreciated!

EDIT: On a side note, I borrowed a loaner compression tester from Auto Zone and it showed 95psi on both cylinders.... but I am not confident in the accuracy as it looked beat to hell. I was going to goto Oreilly tomorrow and see about using on theirs to compare results.

I've read that the more important factor in a compression test is that both cylinders are VERY similar in numbers as this shows both cylinders have worn at the same rate and the actual reading may just be off on the gauge itself. In my case, they gave identical readings, so I'm guessing the actual reading on the gauge is just off. Once I can confirm the reading, I figured I may have to replace the rings, roller bearing, and perhaps pistons. I am curious what you folks have to say before taking off the head to check these out.
 
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Plunkitt

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Nov 26, 2017
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Wenatchee, WA
As previously posted, I bought a 03 Mountain Cat 900 that had sit in a garage for the better part of 3.5 years without being run for $500... I've fixed a few things on it such as the steering nut being disconnected on the steering shaft from the actual steering rod, cleaned carb jets, replaced spark plugs, restrung pull start cord, etc but couldn't get it to actually turn over and start using choke and numerous pulls (with a bit of 2 cycle oil in each cylinder for safe measure). I have checked and all other fluids are good to go (oil, coolant, brake fluid, etc.)

Tonight, I decided to put a little bit of 2 cycle oil in each cylinder and spray a bit of starting fluid in each cylinder to see if she starts. First pull, started right up and of course, smoke was pouring out. I do know that after sitting 2 cycle engines can put out A LOT of smoke. I've read that more smoke is actually better because is shows that the oil is being injected.... it's when you don't see smoke at startup you should worry. I pulled it out onto the driveway and let it run for a minute or so and the smoke started to subside a bit. Also was able to test the mechanical reverse, which works perfectly. Actually I had a hard time not spinning the track on my angled driveway... this machine has a LOT of power! :)

With that said, I've never started up a sled that has sit for the better part of 3 years of not being run. Of course I know the gas is bad and I'm going to siphon as much out as I can and replace with fresh 91octane.

Beyond checking bearings, etc. what should I be aware of with running something like this? Should I just let her run for a few minutes and let the engine burn off carbon deposits, etc or should I not try to start again without checking something?

Any advice is appreciated!

EDIT: On a side note, I borrowed a loaner compression tester from Auto Zone and it showed 95psi on both cylinders.... but I am not confident in the accuracy as it looked beat to hell. I was going to goto Oreilly tomorrow and see about using on theirs to compare results.

I've read that the more important factor in a compression test is that both cylinders are VERY similar in numbers as this shows both cylinders have worn at the same rate and the actual reading may just be off on the gauge itself. In my case, they gave identical readings, so I'm guessing the actual reading on the gauge is just off. Once I can confirm the reading, I figured I may have to replace the rings, roller bearing, and perhaps pistons. I am curious what you folks have to say before taking off the head to check these out.
I'm not 100% on carbed sleds, but for a 900 that seems like a low psi. My old 2005 M7 ran right around 130 psi.


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1Mike900

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Dec 5, 2007
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Bellevue, Wa
Just as long as when it is cold it takes some serious UMPHH
to pull over! Just be easy on the pull cord for the first 10 pulls or so. I did a compression check on mine this last summer, had 155 psi ea. cyl. This was on a 90+ deg. summer evening after work. But both cyl. were identical in pressure which I was amazed! I am sure you held the throttle wide open? If it is hard to pull over, I bet the compression tester is way off! Mine is a "04 also, actually a 03.5 with the later tunnel/airbox etc.. If your running boards have lots of large holes it is the later model, also the airbox has extra holes in the back with very fine mesh screen.

Mike
 
Nov 20, 2017
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When I did the compression check, I wasn't able to hold the throttle down completely as I didn't have anything to wrap around it and was doing a single arm pull on the pull cord. I'll find something to hold the throttle down 100 % and retest it.
 
Nov 20, 2017
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Got another pressure tester and made sure the throttle was fully down this time with a bungie cord... new result is 118psi on clutch side cylinder and 120psi on the other. Still not great, but better than 95psi that I read before. This was a cold engine, so perhaps I'll let it idle for a bit and test again when I have time to siphon out old gas and put in a fresh tank.

Anyone know what Arctic Cat dealers charge for OEM rings/pistons? I've heard they are much better than aftermarket brands like SPI (perhaps not accurately?)... I'm seeing prices hovering around $190 for new pistons, rings, bearings, and gaskets at Amazon (Link Decent deal? Never done a top end rebuild before, but it doesn't look terribly difficult if done correctly.

1Mike900, Apparently mine is a 2003.5 as it has the fine mesh screen over part of the airbox and the large X holes in the running boards. I've read online they made some pretty significant changes/improvements to the 3.5+ models, so I'm stoked it isn't the older model.
 
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Jun 23, 2004
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Black Diamond, WA
You don't need to rebuild it. 120 psi in both cyl is fine. If you couldn't 1 arm pull it over the first time it has enough compression, lol.
Sounds like a great deal if it's in decent shape.
Other than making sure the oil pump is working and carbs are clean, not gummed up where they could lean out a cylinder.
On an older sled, I'd put some fresh premix in it. Rich on oil. And disconnect the oil lines and make sure they're making oil when it's running.
Jet it for the altitude you'll run it at, and make sure it's jetted right, check what's in it.
Maybe clutching.
Those 900s ripped. 150hp, basically as much power as new 800s.
 
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Nov 20, 2017
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You don't need to rebuild it. 120 psi in both cyl is fine. If you couldn't 1 arm pull it over the first time it has enough compression, lol.
Sounds like a great deal if it's in decent shape.
Other than making sure the oil pump is working and carbs are clean, not gummed up where they could lean out a cylinder.
On an older sled, I'd put some fresh premix in it. Rich on oil. And disconnect the oil lines and make sure they're making oil when it's running.
Jet it for the altitude you'll run it at, and make sure it's jetted right, check what's in it.
Maybe clutching.
Those 900s ripped. 150hp, basically as much power as new 800s.


It's currently jetted for a bit more altitude than I intend to run it at (around 8500feet) as it seems to have jets for around 10,000 feet. I live in Colorado, so have some pretty extreme altitude requirements. ;)

premix ratio... 40:1 be ok?

From a google search, looks like most folks recommend running a complete tank of premixed and filling up the oil tank and marking the oil level, then running down a complete tank to see how much oil it used (16-20oz normalish?). Otherwise, I haven't found a good way to test other than pulling off oil pump and running it with a drill to see how much it pumps.... but I'd still have no idea how it's working on the machine. Is that about right?

One more note, I put in a fresh set of plugs before I started all the work on the machine and took em out last night to run the compression test. With the limited run time I have on the machine (around 10 minutes of run time total), they are both tan colored, which would seem to indicate I'm not getting too much oil or too little. Not much of an indication due to run time, but it's something.

By the way, appreciate all the help from everyone. I had a snowmobile when I younger, but haven't had one since early 2000s. The older I get, the cheaper I get, and the more I want to do things myself. Obviously never done most of this before, so the feedback is very helpful. :)
 
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