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Discussion Starter #1
OK you sled gurus... I got one for ya.

1995 Ski Doo Formula STX LT (583 RAVE motor) with 5773 miles (~9288 km's) on the odo I bought used at the end of last season. This thing runs pretty badly during warmup, but after it gets good and warmed up it seems to run just fine. During the warmup it stalls several times (requiring restarts) and bogs badly sometimes (if you try to give it gas, but other times will rev up nicely), and just generally doesn't want to run. After about 10 minutes or so, though, it purrs along like a kitten and runs "normally" and seems ready to hit the trail. Those first 10 minutes are pretty much hell, though. I've never had (or seen) a sled run like this while warming up. It's bad....

What I've done so far that has made NO DIFFERENCE for this problem:
* Rebuilt carbs (new gaskets and washers, new genuine Mikuni inlet valves (needle and seats), new main jets).
* Thoroughly cleaned idle jets and needle jets and rest of the inside of the carbs (w/ carb cleaner, pipe cleaners, toothbrush, and compressed air - you can EAT off their insides!).
* Checked carb floats and float arms - good to go.
* Sync'd carbs.
* Adjusted idle and air screws to service manual specs.
* New plugs.
* Thoroughly cleaned RAVE valves.
* Replaced the Primer.
* Checked all gas lines and primer lines - good to go.
* Had to replace the throttle cable (frayed at oil pump), so that was all adjusted (including oil pump portion) to service manual specs.
* Checked carb boots - good to go.
* Checked airbox - good to go.
* Fuel pump appears to be good to go. Remember, sled runs fine after warmed up.
* Squirted carb cleaner on motor while running to check for air leaks just today - none found.
* I've got no excessive smoke from the motor and no unusual noises that I can detect, either.

Anyone have any ideas??? I mean, what have I missed that would make a difference between running good after warmed up vs. while warming up??


1998 Arctic Cat Cougar
1999 Arctic Cat Z 440
1995 Ski Doo Formula STX LT
 

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well, I think U've established it isn't carburation

I C 2 possibilities, but both are real expensive man, so I would check the carb stuff again.

1) check your compression with the engine cold. see what she reads, pull her over real slowly. then check again when she's warm, and see if theirs a big difference. this would probably be the cheaper possibility, and it is that the inside of the cylinder is worn or scraped, and when she's warm, the pistons and rings are expanding to clsoe the gap.

2) when the oil pump cord was frayed the engine was underlubricated and the bearings are on the go, if that's the case.... it's not good at all. I can still remember pulling what I thought was slag out of a spark plug on an old phazer. popped it outa the plug with a knife, saying to myself "O shit, I burned down the engine, it'll need a rebuild"

then the peice of slag rolled off the counter and across the floor. THEN I realized how deep trouble I was in.

they may be called snowmobiles, but hiding behind that is a cheap excuse to not grass drag.
 

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i wonder if it may be a problem with weak spark, my 96 mxz 583 is starting to d othe same thing, it will start then rev bad and die and as i try to rev it it will bog down, i have press the primer a couple time between each time it stops and after a min or two it will run better and then its fine. i've cleaned my carbs,and check compression bith at 145, thats why i think it may be ignition, it may the the magnetos going out or working pourly at low speeds, with mine if i can get it to rev right away it will be fine then, im not sure what it is though

 

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Discussion Starter #4
Well, crap... OK. I'll go get a compression tester and see what I get cold for each cylinder and then see what the difference is when it's warm. I just know I'm not going to like what I get for readings, either....

Anybody know what I should find in the cylinder?? After 5773 miles, it's prolly pretty worn. Anyone have any good recommendations as to where I can send the cylinders to get bored and honed with top-notch quality and a speedy turnaround time??? Oh, and inexpensively, too??? Not asking for too much, am I???... [:)]
 

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Trying to get blood from a turnip??? LOL J/k man if you want a good bore job and such ide check out http://www.dinesmotorsports.com/boring.htm
or http://www.northerncrankshaft.com/ or http://www.hotseatperformance.com/shop_services.htm for hot seat the prices are HSP BORING (+.010 - .020) $50.00/cyl
(+.030 - .060) $75.00/cyl
(+.070 or larger) $90.00/cyl

those are probably the best places i can think of at the moment not sure on prices but quick turn around times
 

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it is possible that it's a weak spark, but I odn't think that would clear up as it got warm, and I've never heard of anything like that, you never know with electronics tho. and ya, hopefully yer compression is fine and it's neither of the things I'm thinkin.
 

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If your looking for local, try The Starting Line. They're a performance sled, motorcycle and atv shop on College Ave in Waterville. They're also in the phone book. Give them a call and ask for a quote. I've delt with them before, and they seem like a good bunch of guys.
 

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Discussion Starter #8
Originally posted by Tfin70
[br]If your looking for local, try The Starting Line. They're a performance sled, motorcycle and atv shop on College Ave in Waterville. They're also in the phone book. Give them a call and ask for a quote. I've delt with them before, and they seem like a good bunch of guys.
They handle this type of work, Todd??
 

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Discussion Starter #9
Originally posted by Junior
[br]it is possible that it's a weak spark, but I odn't think that would clear up as it got warm, and I've never heard of anything like that, you never know with electronics tho. and ya, hopefully yer compression is fine and it's neither of the things I'm thinkin.
But if it isn't worn or (shudder) broken rings and other nasty things like that... what else that I haven't tried/replaced/cleaned-to-death could POSSIBLY be??? [?]
 

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those reading on my compression are on a motor with 3000 miles about and the entire motor has 5000, mine seams to be running good
 

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Discussion Starter #11
Originally posted by mattgross
[br]those reading on my compression are on a motor with 3000 miles about and the entire motor has 5000, mine seams to be running good
Matt, I can only hope for readings that good. I'll find out tomorrow and I find myself dreading it (although I'd REALLY be lost if it turns out that compression is good and not the problem). Just got back from buying a compression tester. Too late to mess with it tonight.

Wish me luck, guys....

"O Mighty Compression God......" [:D]
 

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It sounds like the carbs are the problem, possibly the pilot jets. If you find your compression is NOT low(should be around 140lbs per cylinder), I'd take a harder look at the carbs. Also crankshaft seals could be getting worn or brittle and not sealing properly. That usually causes the engine to lean out and act like your describing, when warmed they become soft again and reseal again.
Was this sled like this when you bought it?. Are the right jets in the carbs?(some people will lean their carbs for better performance or economy). Thats a few miles on it but if its had good oil in it and decent maintence, if your compression is a little low,(but fairly even) the cylinders probably DON'T need to be bored, maybe just rings. Ski-Doo steel lined cylinders are nearly bullet proof. I've seen them with over 10,000 miles and still well within factory specs.
 

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I don't know if the 1995's still had the primers on the ski-doo's. The ones I had they did and you did 3 prim's before starting, once she starts ease the primer in a few x's while idling her.
 

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Originally posted by ACMan
[br]
Originally posted by Tfin70

They handle this type of work, Todd??
They sure do. As far as I know they do everything from the crank on up. Standard engine work to high performance mods and everything in between.
 

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Discussion Starter #15
Well, I just tested the compression in the motor. 145 psi in both cylinders with a stone-cold motor. So, I'm both relieved and perplexed...

Started up the motor after the compression test and it just acts like it's running out of gas at idle every little while. It'll start to die and the only thing that will keep it from stalling (most of the time) is a shot of primer. Trying the throttle is a guarantee it'll stall out.

modtodd82, you said exactly the only thing left I can think of. Despite being thoroughly cleaned THREE TIMES with toothbrushes and gobs of carb cleaner and wire through the center and compressed air... I'm going to replace the pilot jets. And the carbs are jetted correctly (I increased the mains myself to make the sled safe to -20°F, apparently stock is 0°).

You could also be right about the crank seals, although I've checked 50 times to see if there is any extra oil or crap in those areas and I don't see any. I suppose that don't mean air couldn't get in there, though...

This is SO MUCH FUN... NOT!!! [:)]
 

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One thought about the crank seals. I'm not sure exacly how your sled is set up, but on most that I've seen, the only way to really SEE the crank seal on the MAG side is by taking the entire engine out and taking the flywheel off. On the PTO side, as you know, all you have to do is take the primary clutch off. I don't know, sounds like you've checked about everything I can think of. Just throwing out ideas.

The fuel pump may still be a suspect. I know you say it runs fine when its warmed up. But maybe when its warmed up, there's a good "draw" on the pump, that isn't there when its cold, and the engine is just trying to start. A pump rebuild kit doesn't cost much either, and it wouldn't hurt. Like I said......just throwing out some ideas.
 

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Discussion Starter #17
Originally posted by Tfin70
[br]One thought about the crank seals. I'm not sure exacly how your sled is set up, but on most that I've seen, the only way to really SEE the crank seal on the MAG side is by taking the entire engine out and taking the flywheel off. On the PTO side, as you know, all you have to do is take the primary clutch off. I don't know, sounds like you've checked about everything I can think of. Just throwing out ideas.

The fuel pump may still be a suspect. I know you say it runs fine when its warmed up. But maybe when its warmed up, there's a good "draw" on the pump, that isn't there when its cold, and the engine is just trying to start. A pump rebuild kit doesn't cost much either, and it wouldn't hurt. Like I said......just throwing out some ideas.
Well, I guess the fuel pump COULD be screwing up somehow at low RPM's. Hadn't really thought about that angle. I've been discounting blaming the fuel pump as the sled runs fine at higher than idle RPM's. Might be worth it to keep this in mind if the new pilots don't cure what ails it.

How hard would it be to replace the crank seals??? Is it something I could do myself (never torn a motor down in my life, but get around otherwise OK), or would it go better for my motor to have a shop do it??
 

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its pretty easy actually pto side pull the clutch mag side pull flywheel and stator plate then pull the mounting plate and split the case. all with the motor out of the sled ofcourse only thing im not sure of if they are inner or outer seals
 

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No, its not that difficult if you have patients, general mechanical knowledge, and the time. You'd also need a shop manual to get all the torque specs for everything you take apart. Plus being very organized helps emmensely.
 

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Discussion Starter #20
Ladies and Gentlemen... boy and girls... Gather 'round and LEARN A LESSON!!!

My Formula STX LT is now the very MODEL of a properly tuned and superbly running 2-stroke snowmobile. Picture-book-perfect, in fact.

"HOW???", you may ask??? Aaaaaah... Herein lies the lesson...

After rebuilding my carbs over this last Saturday and testing the compression this morning, it became apparent that my symptoms had changed, somewhat. The sled still wouldn't idle worth a crap and constantly needed shots of the primer to keep it running. And, this no longer changed once the sled got warmed up. So, needing constant shots of raw gas = too much air and/or not enough gas. I decided to replace the pilot jets, which I did just a while ago.

But, I also noticed that the slides were sitting quite high once the carbs were back on the motor after swapping the pilots. So, I grabbed the service manual and decided to check the settings of the carbs. Now, where I made my mistake was when I pulled the carb off the motor and checked/set everything with the carb hanging off the side of the sled. Why? Because when I put the carb back on the motor the change in routing of the throttle cable pulled the damned slide up on it's own!!! AAAHHH!!! And I didn't notice that when I replaced the throttle cable back some weeks ago and did all the setup for the new cable!!!

"AW SH!T!!!!!!!!", says I...

So, using my trusty drill bits to aid me in making sure the slide height stayed correct and equal between the 2 carbs, I redid the calibration and synchronization of the carbs and oil pump just an hour or so ago....

Perfection. Folks, this mofo is just as silky smooth now as a baby's little butt... An absolute MODEL for all... [:D]

I'm so happy I could cry... [:D]

THANK YOU to all who gave me your sound advice. I very much appreciate your time and consideration!!!
 
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