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Old 12-10-2012, 04:01 PM   #1 (permalink)
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1989 ski doo formula MX

I acquired an old ski doo (89 formula MX). had the engine rebuilt; replacing pistons, o rings, new needle bearings...cleaned and set carbs, added oil to gas to break engine in. Ran it for about 30 mins last year at idle and occasionally rev'ed the engine to break it in. took it out yesterday (12/9) on the first snow, it started right up. rode it for about 15 mins at different speed. it was very responsive and lots of power. At the final hrs, i was going to get a little more speed and all of the sudden, it die. Pulled start it couple times before the rope broke. dragged it back to the garage and hooked it to the charger and cranked it, but it didnt start again. changed the spark plugs (they were wet) but still didnt start. any thought as to what happens? need help.
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Old 12-10-2012, 04:59 PM   #2 (permalink)
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Ok, sounds like you're getting fuel. Are you getting spark to go along with it?
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Old 12-10-2012, 06:31 PM   #3 (permalink)
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Start with the easier stuff, check for spark, and a compression test. That sled should fire right up after three squirts from the primer.


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Old 12-10-2012, 08:39 PM   #4 (permalink)
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Check to make sure the tether or kill are OK. If they are, you probably lost spark. CDI's are a very common failure.
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Old 12-10-2012, 09:40 PM   #5 (permalink)
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make sure all wiring is connected (cdi coils ect..) and your switches/ teather are good and no faulty wiring. we will hope that fixes it and you dont need a cdi! fingers crossed for you!
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Old 12-11-2012, 08:31 AM   #6 (permalink)
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Thank you all for your responses. I have done the following last night to check the machine out:
Did the compression test and both cylinders have compression up in the 130+ and holding at the compression.
Checked for sparks and it was all kind of sparks. I used the recommended spark plugs.
one thing that was mesmorizing was the fuel. there was all kind of fuel in the chambers, in the mufflers and leaked out on the floor.
I cleaned the carbs last year and machine ran really nice. I rode it for good 15-20 mins couple days ago without any engine hesitation (in fact it has lots of power).
Looked into the top of the pistons and one has a light tint of color and the other one has a much darker coating (amost black) on the top of the piston.
Is the gas going thru the pump and or float stuck? Any thoughts?

Thanks for your help.
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Old 12-11-2012, 12:10 PM   #7 (permalink)
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Are you storing on a stand?
If you have needle valves that do not seal well, it can leak all the fuel out of the tank through the engine when you have the rear end propped up.
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Old 12-11-2012, 03:50 PM   #8 (permalink)
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The sled is sitting on the ground in the garage. I plan to take the twin carbs out to check and reset it. thanks for the great tips.
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Old 12-11-2012, 08:02 PM   #9 (permalink)
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Drain the crankcase plugs. Even if its not the cause its good to do. Gas/oil finds its way in there, especially if you dont store it with the fuel off. There should be one under each cylinder.

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Old 12-11-2012, 09:04 PM   #10 (permalink)
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If you have excess fuel like that the carbs need to be taken apart and cleaned/checked again. Floats could be sticking


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Old 12-12-2012, 03:46 AM   #11 (permalink)
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There are no crankcase plugs on Rotax engines.
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Old 12-12-2012, 11:26 AM   #12 (permalink)
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How do i get the excess fuel out of the crank case? Is the carb VM 34 352/3? Anyone knows the part numbers for carb kits?
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Old 12-12-2012, 11:52 AM   #13 (permalink)
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Pull the plugs, hold throttle wide open and pull until no more mist comes out the holes.
Put in new dry plugs and fire it up.
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Old 12-12-2012, 03:37 PM   #14 (permalink)
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you guys rock.
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Old 12-18-2012, 09:45 PM   #15 (permalink)
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Quote:
Originally Posted by smallengineguy View Post
There are no crankcase plugs on Rotax engines.
Well i did not know that :P thank you small engine guy for correcting my mistake. Good luck on your sled btw!!!

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Old 12-18-2012, 10:29 PM   #16 (permalink)
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Sounds to me like it could be a bad fuel pump. That explains the discoloration on one of the pistons (washed color because of too much fuel being pumped through the impluse line) same thing happened to my dads stx 583. Pump went bad and then it started filling up the pipe with fuel. Eventualy it cought fire and almost left us stranded. Good thing we were ready for it


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Old 12-21-2012, 02:40 PM   #17 (permalink)
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Quote:
Originally Posted by Snowweasel View Post
Sounds to me like it could be a bad fuel pump. That explains the discoloration on one of the pistons (washed color because of too much fuel being pumped through the impluse line) same thing happened to my dads stx 583. Pump went bad and then it started filling up the pipe with fuel. Eventualy it cought fire and almost left us stranded. Good thing we were ready for it


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I would definatly take it apart and rebuild it. I believe the kits are under 10$. If there are any even needle thick punctures inside it will cause problems.

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Old 12-31-2012, 10:47 PM   #18 (permalink)
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Guys
Got the machine back and running; however, I have noticed the belt slipped when first try to run the sled after sitting over night. It engaged at around 4k rpm. After the initial slippage, it would be fine after that. Is this because of the frozen track or something else?
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