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Discussion Starter #1 (Edited)
I have a 94 STX, starts right up and runs well.

The problem that I have been having, that the dealer cannot seem to fix, is that one cylinder will foul out. It is *always* the PTO side, not the clutch side, that fouls out. Here are the circumstances:

Crusing around on trails just fine. Hit the lake, open it up and zoom for a while. When I get back up on the trail after WOT, and try taking off again, the PTO side will instantly flood out. Pop in a new plug and it will take off again until the next WOT/resume, where it will flood again. Fresh gas, any air temp will cause this.

Here's what I have tried:

Rebuilt both fuel pumps, which are run in parallel and feed the two carbs.

Relocated the fuel pumps to just beside the airbox and under the steering bar from the LAME position under the engine, where it is required to remove the engine to access for service. This move shortened the fuel line path by about a foot to each carb, resulting in better starting.

Cleaned both carbs thoroughly. Like I said, it starts right up and revs well.

Dropping the needle 1 setting on the PTO side.

Swap carb bodies, remembering to change jets because they are different.

Changed out primer, thinking that fuel may be leaking past the diaphragm.

Cleaned both RAVE valves.

Compression is identical (or nearly so) in both cylinders.

I have worked for a couple of dealers in the past, and I just cannot figure this one out. Asking around gets me the same answers that I have already tried, followed by a shrug.

I am to the point that I am just going to have to tear the motor down and replace *everything*.... I hate to do that, because it does run very well before flooding out, I believe that a rebuild is unnecessary.

Any ideas before the teardown???
 

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Have you tried,
putting the fuel pumps back in the stock location.
have ya replaced the needle an seat in the carbs lately?
Even a carb rebuild kit would'nt hurt for a 9 year sled.

what ya have is a carb problem not motor, rebuilding the motor isnt going to help.
by the way, where you above 90 when you did the compression test?

I'd try the above first and see what happens then, there the cheapest and most common.
 

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Discussion Starter #3
Thanks for the reply!

Haven't replaced the needles/seats yet, but figured I ruled that out by swapping carb bodies. The problem did not follow the carb so I figured I ruled that out. When I did the swap, the only things that I swapped were the jets and carb tops (with the slide/needle assembly). The needle/seat stayed in the carb and switched sides with the carb bodies.

Didn't put the pumps back; not inclined to either being they are impossible to service without (pretty much) pulling the engine.

Compression was around 115 on each (I think one was 117).

Brought this issue up with a neighbor; he suggested a couple of things that I want to post here for feedback:

1. Bad spark plug cap.
2. Leaky crank seal.

I do not believe that the caps are removable on this sled like the older sleds (are they? I haven't looked real close yet), but even if they are, shouldn't a person replace both the cap and wire? Are the wires carbon cored, like a car, or are they wire core? If they are carbon cored, I wouldn't feel very thorough without changing both caps and both wires.

Thanks again!
 

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the plug caps, wouldnt hurt to get new ones, get the NGK screw ins. you can change those. as far as the wires goes unless there dried out an cracked, they should be alright.

crank seals, if those were bad then what happens is it sucks air in the cylinder and leans it out and seizes the piston.

do you still have the plugs in it from the last ride, when you sled had this problem?
if you do what color are the ends, white ash - chocolate brown or black and oiley?
 

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Discussion Starter #5
Wires look OK externally. No cracks or anything.

Duhhh... I should have known that... Seals are out of the question then... It ain't lean! ;)

Plugs are black and oily... Indicating rich.
 

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What kind of oil you useing?
you have the stock pipe or an aftermarket?
If stock pipe, have you ever brought the jets size up? (other then the one that needs to be.
The sleds runnin rich, just tryin to figure why.


The jet thing sounds like the Polaris 650 tripple I had, the clutch side had to be one over or the cylinder would lean out and toast it, because of the crappie airbox design.
 

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Discussion Starter #7
Fendrguy said:
What kind of oil you useing?
Stock Ski Doo (non-synthetic) oil.
You have the stock pipe or an aftermarket?
Stock pipe.
If stock pipe, have you ever brought the jets size up?(other then the one that needs to be.
No. Standard jetting.
The sleds runnin rich, just tryin to figure why.

The jet thing sounds like the Polaris 650 tripple I had, the clutch side had to be one over or the cylinder would lean out and toast it, because of the crappie airbox design.
The rotary Rotax has to be jetted differently because of the way that the carbs react to the (clockwise rotating) rotary valve. On the clutch side, the valve opens up at the bottom of the intake opening first, so the vacuum is very high at the bottom of the carb, where the fuel is pulled up from the fuel bowl, giving it lots of gas right away. On the stator side, the valve opens at the top of the intake opening first, so the jet needs to be bigger to respond to the lower vacuum at the bottom of the carb to keep up and to give that side the same amount of fuel as the clutch side.

Newer Ski Doo (and other) sleds that use reed valves normally do not need to be jetted differently, because the vacuum is distributed evenly throughout the carb throat, causing the carbs to react evenly, all other things being the same. I seem to remember some of the Polaris triples (XLT's?) needed the center cylinder to be richer, because the center cylinder ran hotter than the others, being that the others had three cylinder walls exposed to the outside, while the center only had two, keeping it warmer than the outsides. (I don't know why a liquid engine would care, but that is what was explained to me). I've had no experience with the 650 triples, but I can believe that jet sizes could need to be different because of airbox design.
 

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Try runnin KLOTZ oil, Instead of the Ski-doo brand.
useing it in my sled it keeps the plug end chocolate brown, (which is the best burn) and I have NEVER fouled a plug. the only reson I ever change them is about mid season after 7-800 miles, you notice the response is not quite what it was. pull the plug and you'll see the electrode pin has slightly round edges, has a worn look to it. pop in a new set and keep the old for a backup.
Its one of the best oils out there.

try changing your oil over.
Then I bet your Plug fouling will go away.
put in a new set of plugs and drive it for 30 or so miles and check your plugs. you should see a differance.
 

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Discussion Starter #9 (Edited)
Fendrguy said:
the plug caps, wouldnt hurt to get new ones, get the NGK screw ins. you can change those. as far as the wires goes unless there dried out an cracked, they should be alright.
Well, I got new caps and plugs... It's just as bad as before.
crank seals, if those were bad then what happens is it sucks air in the cylinder and leans it out and seizes the piston.
I talked to my local skidoo dealer, and he said that he had one sled that was experiencing the same thing. He said that it took him a couple of months straight working on it to find that the center seal was leaking, causing one side to burn rich but didn't seem to affect the other.
try changing your oil over. Then I bet your Plug fouling will go away. put in a new set of plugs and drive it for 30 or so miles and check your plugs. you should see a differance.
There's no way that I can get 30 miles on it, it fouls out way before that.

Any comments? I am getting real frustrated here! :confused:
 

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I didnt hear from ya for a while, so I figured ya had it worked out.

were you able to ride it at all with the Klotz in it?
if ya can try to just trail ride or around the house anything will help, no WOT though, just want to know what the plugs look like from average use. (trail riding)
then we can rule out the carbs and fuel mix.
because the Klotz wont foul the plug.

if you get a good burn and it still fouls out at wide open throttle then I would move on to an electrical problem.

by the way never did ask, you runnin BR9ES or BR8ES plugs?
bringing up the heat range one to 8's would'nt be a bad idea. it will also help clean up the burn.

try those out and let me know whats up.
 

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Discussion Starter #11
OK, how's this for a theory:

Look at the diagram here:http://216.37.204.206/xtremepowersports/Skidoo_oem/Skidoo.asp?Type=13&A=148&B=4. Note that the drive gear for the oil pump is in between the the pushrods. The gear is bathed in the 2 cycle oil: a big hose goes from this chamber directly to the bottom of the oil tank. Note also that there is an oil seal on each side of this gear, on the crank.

Suppose one is leaking into the engine? This would not only explain the rich-on-one-side-but-not-the-other problem, but if the seal was just barely seeping, then once the engine warmed up and the oil was very fluid, and the seal is softened up, it could seep in and cause this problem.

Any opinions on this one?

Thanks!
 

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OK, maybe I missed somthing above.
is one plug burning brown and the other is black and oily?
From what I understood, I thought both plugs were in the same shape, black and oily.

what your saying about the seal could be. seen some of the damnest things happen.
but when a seal goes it doesnt come back, as in the theory of heat up leak and cool down seal itself.
so if you are riding on the trails and its fine with no plug foul, its the same temp as if TWO on the lake because its liquid cooled.

Before ya go the VERY expensive route on the seal try doing the oil change over and trail ride only and see what ya get on the plug.
 

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Discussion Starter #13
I think I may have found the problem. I talked to a local mechanic, and he said that it sounded electrical to him. So, I came home and checked all of the electrical connections on the sled. The wires connected to the coil were kind of loose, so I pinched them tighter and reconnected them. The sled started right up and ran well.

I guess I won't know if this is the solution or not until I get some snow and a chance to put some miles on it. I am going to try the Klotz oil once this tank gets down to the bottom.

Thanx everyone for the help, and I'll keep ya posted.
 

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Discussion Starter #14
OK, I got the problem solved. I went to a local mechanic and asked his advise. He said that the problem sounded electrical. Suggested that I check out all of the electrical connections on the sled before bringing it in to be repaired. So I did.

Took about an hour, and I didn't find anything wrong. All the connections seemed good, and most were tie strapped together so that they couldn't vibrate loose. After scratching my head in puzzlement, my eyes fell on the coil. I removed the coil to see how the connections were fastened to it. There is a really nice rubberized tie-strapped connection connecting the coil to the stator, but I wasn't sure how the coil was connected to this wire. On the bottom of the coil, there were two wires connected with *spade connectors*, and one of them was almost disconnected!! Why put a nice rubberized connector out in plain view when the coil is actually connected with spade connectors???

Anyway, I cleaned all the grime off of everything, pinched the spade connectors tight, and pushed them back on to the terminals. Lo and behold, the thing started up and ran!!

Put on 40 miles on Sunday. No fouls! Lotsa power! Problem solved. I think I am going to take that coil back off and solder those connectors on so that it cannot happen again. Pretty idiotic having a failable connector like that connected to a wire with a quality connector, huh?

Thanks for the suggestions everyone.
 
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