I have a 95 mach 1 with a rotax 670. i let it sit for a week, and when i returned it started up just fine when i ride it, she wont go past 7 thousand rpm or 100 km. when useually i can get 8 and three quarters and go 160 km. and now if its warmed up and i drive. if i slow down to less than 5 km and try to take off it will only run on 1 cylinder. then with a little trottle fiddling it picks up again. i have replaced plugs plug wires and coil. didnt help.     any one got a clue

[Edited by Klide on 2/18/2008 at 6:29 PM]

Posted by Klide

Posted by runrotax
I have a 95 mach 1 with a rotax 670. i let it sit for a week, and when i returned it started up just fine when i ride it, she wont go past 7 thousand rpm or 100 km. when useually i can get 8 and three quarters and go 160 km. and now if its warmed up and i drive. if i slow down to less than 5 km and try to take off it will only run on 1 cylinder. then with a little trottle fiddling it picks up again. i have replaced plugs plug wires and coil. didnt help.     any one got a clue

      

Well Im a cat guy but I would wiggle the throttle when it acts up and if it helps or fixes it then it may be a bad throttle monitor that’s what the problem usually is with the cats, on the cats you can bypass the monitor and it will work fine but im not sure about skidoo. Also on sleds with round slide carbs there is a magnet in the slide valve that indicates the throttle position by sliding in front of a sensor and if the magnets came un glued it can cause a weird problem like that to. If that’s not the problem then I would be thinking about either a stator or a crank case seal. One way to check if its a crank case seal is to choke it when its at its maximum operating temp and if it runs better then is almost 100% a crank case seal. The reason it would run better is because if its a bad crank case seal its sucking in more air causing it to run lean. If it does run better by choking it I would first clean the carbs and if that doesn’t work then  I would do a pressure test on the motor and that is when you pull the carbs off and pull the pipes off and cap them both with special caps you get from the dealer but you may have to have them do it because they will not always sell a customer factory tools. Then you take the black hose/pulse tube coming off the motor going to the fuel pump and put about 5-7 LBS of compressed air in it and if it can not hold that for lets say 5-10 min then you have a bad crank case seal. I would do a compression test first though you may have blown it up. Cats are usually about 120lbs-145lbs per cylinder depending on the sled but check with your dealer for compression specs. Each cylinder should be within about 5 lbs of each other. Also make sure your fuel system and carbs are cleaned out and you have a good fuel supply. Hope this helps keep us updated.

Tahnks for the tips. I have tryed compression and both cylinders are sitting at 130 psi. I have a feeling that i have a crank case leak is right. but what you said about diagnosing is the problem. you said to choke it at full operating temp i dont have a choke on my sled. it there another easy way to tell?

 

You could try to prime it but that may give it to much gas and kill it. The other way is to take break cleaner and spray it around the crank case where the 2 halves meet while its running and if it runs better then you have found your leak. There is another way involving propane but I’m not exactly sure how to do it I think you just have a propane torch and go around the crank case and the vapors from the leak will catch fire. I don’t think it sounds to safe but a lot of other mechanics say it is and they say it works but like I said I’m not exactly sure how to check that way.

im no expert but my dad kind a has the same problem he has a 1999 summit 670 rotax. ive talked to some people and they all said to check the rubber boot that comes from the carb to the motor. and im not shure if that year has it but check the billows in the very front of the motor