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Discussion Starter · #1 ·
1999 Ski Doo MXZ 600 roughly 3,500 miles (I have another matching sled to this one so I can swap parts)

I need help friends! I've tried about everything I can think of and I'm going crazy. I'm fairly mechanically inclined but I'm really new to snowmobiles. Please help. SOS

12-31-2019

First trip of the year, the carbs were cleaned out and some general maintenance was done. We rode both sleds 70 miles with ZERO issues.

Came home and put the sled in the garage to replace the carb boots (cheap amazon boots) and I added aftermarket Hot Grips to the sled since the the stock ones no longer worked. Checked the reeds when the boots were replaced and they looked great, no chips and they laid flat.

2-8-2020

Took the sleds to northern Michigan to go for a ride, started them up on the 3rd pull and warmed them up for a few minutes then took off across the lake to the trail head, everything seemed fine. When we got to the trail head I noticed my fiance's sled was sounding weird and instantly thought it was running on 1 cylinder. I changed the plugs because they look exactly as the picture shows, 1 really good spark plug with good color and burn (PTO side) and the other looks like a brand new plug. It didn't show it running lean and it didn't show it running rich. It literally looks like its not sparking and just covered in fuel (MAG side). So I took off on the sled and ran it hard and fast thinking I could clean it out and it would run better. I drove it for 40 miles and the whole time I swear its on 1 cylinder. It doesn't drive too bad like its still got a little power but its boggy and you can hear it almost "knocking" or sounding hollow and feel it. If you get it past the bog and hit WOT it will lift the ski's up and go like its on both cylinders (but I have no idea if its firing on both I was able to hit 50MPH without much problem) and it sounds good but, its clear from idle to 3/4 throttle its on 1 cylinder. After the 40 miles trip I pulled the plugs and they looked the same as before, the picture attached is after 40 miles.

Came home, put the sled in my heated garage and started the investigation.

Compression check was done with 5 pulls each time, both plugs pulled, I did not hold it WOT, cold engine. 5 tests per cylinder

- MAG Side: 115-121

- PTO Side: 123-129

Both carbs were taken off and sprayed out with carb cleaner. I attempted to replace the needle and seat but I could not drive the pin out. I replaced both jets on both carbs. They looked fine and were not clogged but I replaced them anyways.

- Put everything back in the original place with 2 fresh plugs.

- I then swapped the carbs keeping the fuel lines the same.

- I then swapped fuel lines.

- I pulled both fuel lines off and started the sled and both lines produced the same amount of gas with a steady flow.

- I then swapped 1 carb off of my sled that's in good working condition

- I then swapped fuel lines. Every time I take the fuel lines off gas comes out so I know its getting fuel to the carbs

None of this worked, every time I tried something new I started the sled and lifted the back up and let it idle then did a couple hits then an idle and a shut down to look at both plugs. When I pull the plug out of the MAG side white smoke will come out for a minute or two and you can visually see the top of the piston is wet.

NOTE: At the beginning of the year the MAG side of the sled did have an issue where after it was shut off the carb would continue to puke gas out of the overflows. I took the cap off a couple of time and it never happened again. (no idea what caused this but maybe its important)

After more thinking the plug wasn't showing fuel problems its showing more of a spark issue. Both plugs were pulled and tested on the head and show good spark. Both firing at the same time and both good blue spark. Just to make sure I purchased a used coil and swapped it out with no change. I took the coil off of my sled and still no change (I swear it sounded better and acted a little better but I don't think it was). I even changed the plugs out again to make sure it wasn't a bad plug. I took the coil off of the tank and swapped wires and still no change. I can pull the plug wire off of the MAG side and the engine does not change tune and continues to idle, if I pull the plug off of the PTO side the engine dies instantly. This happens with all 3 coils.

After all of this testing I can touch the Y pipe on the MAG side about an inch away from the head and its warm like I can leave my hand it and not get burnt but if I try that on the PTO side it will burn me.

Something else I've noticed that might be related is when I started the year both headlights worked, when I started day 1 of testing the low beam stopped working, when I started day 2 of testing the high beam no longer works. The dash lights and tail light work still, when the RPM's are low they are dim but as soon as I hit the gas they turn up. All of this testing was done with the hand warmers and thumb warmers turned off.

I'm so lost with what to do next. I can swap MPEM boxes from my sled does that require anything else? I'm assuming I would have to swap the tether as well? Just at a loss with where to go next.

Please help...
 

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If you swap boxes you'll need to swap Dess keys too. Try that but if your blowing bulbs you may want to swap voltage regulator as well but do one ant a time so it's easy to pin point issue. Are you gapping you're plugs?

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You have two sleds the same. Take the carb off the good one and swap it onto the one you are having problems with.

Lynn
 

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Discussion Starter · #5 ·
If you swap boxes you'll need to swap Dess keys too. Try that but if your blowing bulbs you may want to swap voltage regulator as well but do one ant a time so it's easy to pin point issue. Are you gapping you're plugs?

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Is the Dess key just the tether or is there another box somewhere that needs to be swapped as well? I have not gapped the plugs I was always told it will take the coating off and to never do it. I'm just trying this all 1 at a time so I can pin point the issue. Could the voltage regulator not be sending enough spark to the MAG side? Seems like any amount of spark should be igniting the fuel.

When you swapped coils did you use different wires and caps or the original ones?

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different wire and caps each time. I pulled the coil off as an assembly each time.

You have two sleds the same. Take the carb off the good one and swap it onto the one you are having problems with.

Lynn
I did that but it didn't work. If it was a fuel or a carb issue wouldn't the spark plug show it running too lean or too rich?
 

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I missed where you said you had already swapped the carbs. You only need three things for your engine to run. Compression. spark and fuel if the engine is in good condition. You have all three essentials so I'd be looking further into the engine suspecting a crank seal being bad and leaking air into the cylinder.

I don't believe the headlight issue is related to the running issue but it may be.

Lynn
 

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Yes just swap teathers. Regulator should take care of lights. I doubt regulator is affecting spark the weird thing is if you were lacking spark/power off your stator it wouldn't clean up at wot. That's kinda why I was thinking caps and or wires for plugs may cause this

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I missed where you said you had already swapped the carbs. You only need three things for your engine to run. Compression. spark and fuel if the engine is in good condition. You have all three essentials so I'd be looking further into the engine suspecting a crank seal being bad and leaking air into the cylinder.
I don't believe the headlight issue is related to the running issue but it may be.
Lynn
I agree with Lynn. Should definitely take a look.

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"I have not gapped the plugs I was always told it will take the coating off and to never do it."

You've never gaped the plugs?!?!?! I've never heard of any coating. Always gap your plugs to your owners manual specifications.
 

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You always gap your plugs be very careful to not over stress them but it's just one more variable to remove from the equation as that's how it was designed to run NGK's are usually not far off for your application but couple thousandths would change things. You can get a gap tool at any parts store for less than 5$ and make sure you use it correctly as it is very easy to go to far and over stress.

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Discussion Starter · #11 ·
I missed where you said you had already swapped the carbs. You only need three things for your engine to run. Compression. spark and fuel if the engine is in good condition. You have all three essentials so I'd be looking further into the engine suspecting a crank seal being bad and leaking air into the cylinder.

I don't believe the headlight issue is related to the running issue but it may be.

Lynn
No problem! That's what I was thinking as well. I have all 3 so it has to be something further down the line. My question about air leaking into the cylinder is wouldn't my plug show it running lean? When too much air gets into the engine does it still run on that cylinder or is it too much air to spark?

You always gap your plugs be very careful to not over stress them but it's just one more variable to remove from the equation as that's how it was designed to run NGK's are usually not far off for your application but couple thousandths would change things. You can get a gap tool at any parts store for less than 5$ and make sure you use it correctly as it is very easy to go to far and over stress.

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Just what I was told as a kid and always believed lol I guess I was lied to!
 

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There is some truth to not gapping certain spark plugs. This is the case with Iridium plugs found in newer vehicles today. If you use a gauge to check the gap there are special plastic gauges to do this with. A metallic or even brass gauge can damage the thin layer of Iridium off the electrodes.

Lynn
 

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It was just the rotary valve motors that had different size mains. The reed valves were the same if i am not mistaken

No spark at low rpm could be a stator starting to break down. With higher rpm. The frequency and higher voltage will push threw for now. But will get worse. Ohm it out and check to ground as well. Good luck.
 

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This is very interesting the 600 is a pretty solid engine im pushing 6k on my 600 with just carbs an a new recoil i call her old faithful because she just run so good allways.

Gap your plugs to be safe can double check your carbs just to be safe. Dose your sled have dpm?

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Spark gap isn't the problem. My money is on the stator given everything else you have done/checked. (Isn't really anything else left.)
 

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Discussion Starter · #18 ·
Spark gap isn't the problem. My money is on the stator given everything else you have done/checked. (Isn't really anything else left.)
thank you, I don't think spark gap or anything with fuel or the carbs is an issue because my plugs don't show a fuel issue (lean or rich) they show a not sparking issue. I'm beginning to think that as well. I have read on a few other forums that the voltage regulator could be a major issue in these things especially since I have had 2 headlights burn out in the last week when doing testing. I think I'm going to look up how to test the stator this week. If that checks out I'm going to replace the voltage regulator and then the MPEM box from my other sled to see if anything works. I'll replace 1 at a time until it works.
 

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Discussion Starter · #19 ·
The older motors were like that, but the newer series 3 motors(600/700/800) run the same main jets.
Ditchbangr looks like you have found my post. I'm at a loss with what to do next. I was thinking stator but wouldn't that effect both cylinders? Also if it was the voltage regulator would it effect both cylinders since I have 1 coil pack? I mean I have blown the high and low beam headlights so I think I have a voltage regulator issue I'm just wondering why the dash lights didn't blow before the headlights if its a voltage issue. I've also been wondering about a crank seal but I don't get the high idle issues others have and the spark plug doesn't show a rich or lean situation.
 

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Don’t think it’s the regulator at all. Definitely think it could be the stator, or bad wiring somewhere for your spark issue. A leaky seal wouldn’t have much to do with the spark issue either, but would definitely be a bad issue to have a well.
 
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