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Old 11-22-2012, 06:30 PM   #1
amcross OP
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Thumbs down Help! Sherco 125 (06) Revs Out Of Control Suddenly ... Throttle Cable Issue?

A friend of ours just purchased a used 125 sherco, 2006 model year. We know the former owner, he never had a problem with this as far as we know.

twice today, the bike suddenly revved up SIGNIFICANTLY with no provocation, while ridden by a novice rider using very little throttle (once was a crash, once was a nice save by a very rattled rookie!); (Mike guestimates that it was sticking at, for example, 1/4 throttle ... and thus continuing to increase RPMs/accelerating.) (to be clear, I don't mean a simple small increase in RPMs like my GasGas does as it's running out of fuel ... this was a significant jump and continued to rev higher and higher)

then Mike (my hubby/our mechanic) rode the bike and eventually was able to repeat it. When it revved, he could snap the throttle several times until it shut back down.

no binding whatsoever at full lock either direction.
the throttle cable had a small amount of excess freeplay which he removed. still could make it stick and scream. cable is good otherwise.
We found that, when an adult rider is sitting on the seat-less seat area (not on the fender), the tank actually could pin the throttle cable. Zip tied the cable (loosely) to a segment of frame that keeps it away from said pinch point. Not certain if the bike reved out again after that adjustment.

Obviously, the new rider is nervous to get back on her bike, and Mike is nervous to let her ride it again until we're certain the problem is solved.

has anyone seen anything similar? any ideas what could be happening?

HELP????
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amcross screwed with this post 11-22-2012 at 06:37 PM Reason: correction/clarification
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Old 11-22-2012, 06:51 PM   #2
lineaway
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Quote:
Originally Posted by amcross View Post
no binding whatsoever at full lock either direction.
the throttle cable had a small amount of excess freeplay which he removed. still could make it stick and scream. cable is good otherwise.
We found that, when an adult rider is sitting on the seat-less seat area (not on the fender), the tank actually could pin the throttle cable. Zip tied the cable (loosely) to a segment of frame that keeps it away from said pinch point. Not certain if the bike reved out again after that adjustment.


HELP????
Put the free play back,(Mike might not like any freeplay but a newbie needs a little) remove the zip ties. Check throttle tube, check cable for wear, check connecting point at top of carb, and check carb , slide, idle adj. screw. If nothing is found, find another Sherco and compare cable routing. Nothing worse for a begiining rider is a bike scaring the crap out of them.
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Old 11-22-2012, 07:09 PM   #3
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Hey lineaway,

There was enough excess that the throttle end of the throttle cable was close to being able to pop out of the trottle housing and hang. I am dont think this was the problem but am not sure. The throttle cable out the top of the carb you know the 45 degree bend was setting against the tank. This meant that when the tank moved it pushed the bend over just a bit. Again not sure if this was the problem. But a loose ziptie pulled the cable over so the tank does not touch it any more. I would like to get a look at another bike to see the routing. Not another one close to us. Maybe someone can take pictures for us.

Thanks
Mike
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Old 11-22-2012, 07:32 PM   #4
lineaway
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Are you missing the little rubber boot that holds the cable into the 45 bend?
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Old 11-22-2012, 10:16 PM   #5
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Had a similar problem on a Honda motocrosser back when I rode an arenacross BITD. After much frustration and loss of confidence we found evidence that the carb slide had a burr that was catching in its track. This was a flat-slide carb, and I don't know what carb you are dealing with, but if you find no evidence of the cable hanging up (far more likely) look for signs of scuffing on the slide and its path.
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Old 11-23-2012, 01:45 AM   #6
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Are you missing the little rubber boot that holds the cable into the 45 bend?
The rubber boot is there.
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Old 11-23-2012, 01:51 AM   #7
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Originally Posted by ridenm View Post
Had a similar problem on a Honda motocrosser back when I rode an arenacross BITD. After much frustration and loss of confidence we found evidence that the carb slide had a burr that was catching in its track. This was a flat-slide carb, and I don't know what carb you are dealing with, but if you find no evidence of the cable hanging up (far more likely) look for signs of scuffing on the slide and its path.

I will pull the carb apart today and check for any stiction. This one has really got me baffled, the throttle cable seems fine although I have not removed it from the bike to give it a complete visual. I will get that done today.

Thanks for the input.

Mike
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Old 11-23-2012, 06:36 PM   #8
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So I should have just taken everything apart when the problem started. I found two things wrong and am pretty sure the problem is fixed.

1st The top of the carb was put on 180 out. This caused both the spring and the cable to be off angle inside the carb.
2nd I checked the airfilter to get and idea if the intake was clean but did not pull the filter to check. If I would have I would have found a fair amount of grit inside the airbox. There was enough grit on the slide to cause it to hang up. So after cleaning out the airbox the carb and greasing the inside of the airbox so it cant happen again the bike seems to be doing fine.

I know better to buy a used bike and start riding it without checking everything over. This was a great reminder to me to take the time to check everything over before riding.

Lesson learned.

Mike
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Old 11-23-2012, 07:30 PM   #9
lineaway
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Hopefully it stays fixed!
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