On a properly working sled, a common way to quickly check whether the motor is running rich or lean is to do a good full-throttle run with the sled, shut it down, then pull the plugs. You want the porcelain tips to be a light brown or tan colour. If they are very dark, or black and carboned up after a high speed run, then you know you're running too rich. However, if they are very light tan, almost "off-white", that's when you know you're running too lean (it's better to be rich than lean).

Crank seal failures are sort of common on snowmobiles, and definitely a likely cause for melting down 1 cylinder and not the other.

 

Nope it's the other cylinder oppsite the clutch. Well sounds like we better look into that crank seal.....How would the crank seal affect the gas and make the one cylinder run lean?? Is it letting extra air past the piston ring causing a lean condtion?? But that don't seem right though because you would think it would let oil through not air. I think getting this to run right and last may be a bit over our heads!! But this is the only way we are going to learn!! Even if it the expensive way to learn

 

that thing could have died for a number of reasons. 2 strokes dont live long running lean. I would recomend cleang/rebuilding the carbs and make sure the fuel system isnt plugged or restricted anywherea new fuel filter is a good idea. maybe jet it a little richer to be safe.

welcome to snomobiling, you ride for 2 hours and wrench on them for 8. especially older sleds.

DJ

 

Yea you shure got the wrenching part right!!!! I told him from now on he had better keep a close eye on things like looking at the plugs every time he fills up and to try and listen to the motor while riding........Well live and learn I guess Thanks

 

Remember, 2-strokes don't work like 4-strokes.......there is no oil reservoir in the crankcase like a 4-stroke. With a failed crank seal, air will get into the crankcase, and that is where the normal fuel/air mixture first comes into the engine before it is pushed into the combustion chamber on top of the piston. If the seal is gone, too much air will get in, and lean out the fuel/air mixture.

Snowmobiles are very "finnicky" though...........my dad and I were just trying to mess with his today to get rid of an annoying bog at low RPM's, just off idle. My ZR 700 absolutely stomps his ZRT 600, but they should run closer together than they do. My dad thinks that maybe he needs to play with clutching or something on his to make it take off better, 'cause right now it's a complete dog out of the hole. We might actually trade clutches to see if that makes a difference on his.

 

Thanks Captin Pete!! I did some looking around on the internet on 2-stroke motors and got a better feel on how they work....so now I see what you are talking with the crank seal. But I do have one more ?? All the info I found was basicly dirtbike motors and they were showing the reeds open to let fuel in....so my ?? is do these snowmobile motors use reeds?? If so is it something we should look into?? Man I feel like such a newb Thanks

 

A common thing people overlook is what type of gas their sled takes. I am not talking octane, but whether it has alcohol in it. That can burn up a motor real quick if you fill up a whole tank with it. A friend had that happen to his after filling up at a gas station for the first time. You should check the station he filled up at it, and see if there is a sticker on the pump.

It doesn't really matter in cars, since they aren't made to perform like most snowmobiles.

Just an idea