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Only one cylinder working?

11749 Views 11 Replies 8 Participants Last post by  Sled_Dog
Hey guys,

I'm pretty much a novice snowmobiler and I have a 1990 Jag 340. I leant it out to someone to tow a buddies ski doo and he said that he "dropped a cylinder" on the way out. As my snowmobile has two cylinders I assume this means that one stopped working. I changed the plugs, one looked really dirty, but don't know how to tell if it is working properly now or not. What are the characteristics of a machine only working on one cylinder and what are the possible causes/fixes.

Thanks for your help,


BTW didn't mind lending it out cause I got a new Z 570 too :)
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well is one of the plugs wet? he wanted to tow with a little 340 fan? wouldn't be surprised if you blew a cylinder trying to do taht. or is that what he did? whatever that wouldn't surprise me. Snowmobiles don't make the greatest towing machines. In my and most ppl I knows opinion anyway. Do you know how to do a compression test? I would take it to a local dealer and have them compression test it. You will be able to tell if both cylinders aren't right. Take it for a rip if it bobbles and isn't running well then gues what?
Best bet would be do a compression test. If they are out of whack, you've probably got a toasted cylinder on your hands.

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Me again,

When you say "bobbles or isn't running well", how bad should it run on only one cylinder? One of the plugs looked VERY different from the other one. Coated in black even on some of the threads. The other one looked relatively clean. Could this plug have been the problem or is it likely more serious?

Thanks again.

if there is junk on a plug, that usually means it is not firing. Try new plugs, check the spark.

I Love B&M Coasters.
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Ws the plug just black, or was it wet also? Maybe it is flooding from too much oil or something.

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I've seen spark plugs load up like that from being asked to work that hard with out getting a chance to rev. Hopefully thats all it is just a bad plug.
If you don't have a compression tester, give it the field test. Take both plugs out, put your thumbs tightly on the plug holes and have someone pull the rope.If it doesn't push air past your thumb on one of the holes, that is the bad cyl. If both are good look towards a dirty carb on a two carb sled and at the coils too.Put new plugs in the boots and lay them on a head bolt or some other source of good ground, pull the rope and look to see good bright blue spark from both sides. Ps. its easier to see with the garage lights off. Try these things and LMK.

Mean Green Racing
Elyria, Ohio
if it's only running on one cylinder it will have an extreme power loss and not rev fast or quick, especially with a small displacement engine. Usually there will also be a deep bogging noise from the carbs. You couldn't not notice it only running on one. ohhhh yes also after it's good and warm drop some snow on each side on the Y-exhast pipe and see if both pieces melt.
Thanks for the help people,

Put some brand new plugs in and it seemed to do wonders. Pretty much sure she was firing on both. Bought a compression tester, HAD to check it out for sure. Both cylinders were registering about 105 psi. Not great, but she's an old machine.

So I think the plugs were the cause, wheew. $6 for plugs was better than dealing with a blown cylinder.

Guess it goes to show you gotta respect your old machine too :)

I think part of the problem is that I bought a new machine with twice the hp and displacement. This was screwin up my perception of what an old 340 actually runs like.

Again thanks for all your help,

After all this is the best way to learn about this stuff. Beats having a dealer stick in new plugs and charge me for a new cylinder :)

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<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>Originally posted by chiefkp:

Beats having a dealer stick in new plugs and charge me for a new cylinder.



Don't trust the local dealers very much? Sounds like you have had bad experience with them before.

Trees don't make the greatest brakes...
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in the modern world you never know who you can trust
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