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Thread: Runaway engine

  1. #1

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    Runaway engine

    I got this ski from a guy that could'nt get it running.
    When I got it it was running on one cyl(back) and would not rev up. comp is 150 both cyl The engine looks like a fresh Rebuild never run.I did a crankcase pressure check holds 10 psi. reeds are new. When I rebuilt the carbs I found the low speed jet was missing from the front carb. I took one from a spare set and reinstaled the carbs. I also replaced the coil. When I started it it wouldn't start so I blew in the tank vent to pressurise the tank. When it started the rpm ran away the first time I was able to pull the lanyard to shut it off the second time I had to open the throttle then it backfired and quit when I tried to start it again it was locked up and wouldnt turn. I let it cool down pulled the plugs put a little oil in the holes and was able to get it spinning free. Still has good compression. Now I'm scared to start it again.
    Any ideas?


  2. #2
    All hail the Chief! fullboogie's Avatar
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    Massive air leak somewhere - you have to find it before you go further. The backfire may have damaged the reeds too, so plan on pulling those off.

  3. #3

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    I cant figure where I tested the pressurised the crankcase held 10psi for 10min. any Ideas?

  4. #4
    If your not doing something, its hard to screw up. stlouisramsfan's Avatar
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    doesnt it also runaway when starving for fuel? also make model year etc helps...
    Last edited by stlouisramsfan; 09-08-2009 at 04:41 PM. Reason: typed air instead of fuel....

  5. #5
    mrbtd's Avatar
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    Sounds like a lean runaway there was enough fuel to start it but not to keep it cool. It will happen sometimes when going through a carb rebuild or redoing the fuel lines.

    If it were me....If it did it once I would be ok. Twice and I would look @ everything.

  6. #6
    Happily Self-Employed WFO's Avatar
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    Quote Originally Posted by mrbtd View Post
    Sounds like a lean runaway there was enough fuel to start it but not to keep it cool. It will happen sometimes when going through a carb rebuild or redoing the fuel lines.

    If it were me....If it did it once I would be ok. Twice and I would look @ everything.
    +1

    first check the throttle linkage/cable to make sure the carbs are at true idle

    then prime the carbs by either cranking (hold the start and stop at the same time... it wont fire) until fuel is constant thru return line into the tank, or use a suction to pull fuel thru the carbs via return line

    after you confirm the it is at true idle, and carbs are full of fuel, and it still tries to runaway, then look for an air leak

  7. #7

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    make sure you have some play in your throttle cable. if it's tight, your carb valves may be slightly open under idle, which can cause a run away under no load.

  8. #8

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    also check and make sure plugs are tight. mine ranaway, then i realized one plug wasnt all the way tight. I use the method of 1/4 turn after hand tightening.

  9. #9

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    The ski is a 2004 xl700
    I saw somewhere to bleed the carbs take the return line off the carb and blow on it till gas comes out the carb. Will this work?The restrictor hole in the return line looks so small it would take forever.

  10. #10
    Ride a day, wrech a week!
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    this is a common problem with high performance standup motors....the fastest way to stop it is to hold it wide open.....i know this sounds funny.....but it will stop it....pulling the plugs won't do it....and killing the lanyard won't do it.....you have an air leak or it's only getting a tiny tiny bit of fuel....it's scary has happend to me a few times, once on the ramp loading them on the trailer....just don't panic and hold the throttle wide open. it will stop it.

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