dakh Posted October 23, 2018 Report Share Posted October 23, 2018 Hi folks, First post and a question, I know somewhat lame but I got a pretty strange thing going, hoping this is some kind of a known issue.. I got this 2017 Contact ES, for a girlfriend, that decided later she can't hack dirt bike riding after all, so I figured what the heck, let me go ride it myself. The bike is essentially new, maybe 2 hours run time. I go with my usual riding buddies to Walker, carry 2 extra 750ml bottles of premix. After adjusting to it for the first half hour, I'm starting to giggle and have a ball picking the most gnarly line I can see and still making it.. After a while I go up this rooty ledge and all of a sudden the darn thing just starts revving to the moon. I get spooked, stop, put it in neutral and try to see if I have a stuck throttle. Doesn't appear to be the case. I hit the kill switch. No, still screaming its nuts off. Pull the spark plug wire. No effect, still screaming! My buddy has caught up to me and is looking at this **** in disbelief. I click a few gears up and drop the clutch, it stalls. Ugh. Ok. Some coolant leaked out, not that much but noticeable. Wiggled some wires, waited a bit for it to cool off, nope, won't start. Wiggled some more wires, tried to start it a bunch of times, it seemed to want to catch a little here and there but definitely no go. So I had a dead engine race down the mountain, brought it home. Pulled the spark pug, it looked perfect, and has spark. But won't start still. So first, if it ran for maybe half a minute in this "runaway mode", do I need to now be concerned with internal engine damage? Second, what's a good sequence for figuring out why won't it run again? Third, how do I prevent this from happening again? I'm planning to call a dealer when they open but not sure if this would be something covered under warranty. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted October 23, 2018 Report Share Posted October 23, 2018 you've probably sheared the flywheel timing key 1 Quote Link to comment Share on other sites More sharing options...
tony27 Posted October 23, 2018 Report Share Posted October 23, 2018 Sounds like you had it dieseling which can do damage to the piston & rings. As feetupfun says I'd remove the flywheel first to check the state of the key before pulling the header pipe & looking up the exhaust port to check piston condition For the revs to rise like they did there are only a couple of things that could be the cause. Either the throttle cable was displaced at either end meaning the slide couldn't return fully or less likely you had a major airleak develop - would need to be something like the manifold coming loose/split but airleaks normally don't just suddenly happen Quote Link to comment Share on other sites More sharing options...
section swept Posted October 23, 2018 Report Share Posted October 23, 2018 (edited) 2 hours ago, feetupfun said: you've probably sheared the flywheel timing key That would stop the engine. For the engine to run with the HT lead pulled off the plug and the throttle closed the engine would not be able to run. No spark and idle fuel only. With the timing key sheared the ignition pick up might get wiped out but without the flywheel rotating there would be no spark. To let the engine runaway there would need to be an internal component glowing to ignite any fuel and a massive air leak between the carb and inlet port. If there was sufficient fuel in the crankcase then the engine would have consumed this very quickly and died. Endoscope through the plug hole to inspect cylinder bore, potentially check compression thumb over hole or with a gauge. Kill switch needs to be investigated. Excess carbon build up could provide glowing particles to act as ignition source. New bike not yet fully run in (bedded in) could be anything. Edited October 23, 2018 by section swept Quote Link to comment Share on other sites More sharing options...
lineaway Posted October 23, 2018 Report Share Posted October 23, 2018 (edited) The flywheel shears as the engine shuts down. Pull the exhaust header. Look at the piston and rings. You have likely nipped the piston. The cylinder should still be good, but new piston and rings. P.S. Hydrochloric acid can clean up the aluminum in the cylinder. Edited October 23, 2018 by lineaway Quote Link to comment Share on other sites More sharing options...
pauls320 Posted October 23, 2018 Report Share Posted October 23, 2018 Ouch!, sounds like the throttle cable outer sleeve got pulled out of its base..if not a branchy ride area, I would look at a improperly routed cable..maybe poorly positioned zip tie job that made turning steering hard over pulled cable out?? Its a horrible sound when ya hear a runaway motor howling and then abrupt silence...they diesel and run even without ignition intact so its best to quickly smother exhaust outlet completely with gloves or whatever is handy (obviously only if rear wheel is not spinning wildly) Good luck and hope the carnage is minimal Quote Link to comment Share on other sites More sharing options...
dakh Posted October 23, 2018 Author Report Share Posted October 23, 2018 (edited) Thanks for all the replies! Looking a big grim though... I don't think there's anything wrong with the throttle mechanism, but will check the slide position. It snaps back good and was snapping back fine as it was "running away". Engine seems to have very good compression still. Can you explain the flywheel key shear theory a bit more? I don't see how would that explain the runaway, or how would the runaway shear it if that is what the theory is. If it currently has spark (it does), that means the flywheel is still spinning together with the crank isn't it? So far I found one guy who had this happen on a txt280, same thing still ran at high RPM with spark plug wire pulled. Same thing had to kill it with the clutch. Also was running out of gas so seems lean condition was involved in both cases. His did restart after that just fine though. Edited October 23, 2018 by dakh Quote Link to comment Share on other sites More sharing options...
pauls320 Posted October 23, 2018 Report Share Posted October 23, 2018 The throttle cable sleeve slides into adjuster on carb end and socket on twist grip end and will still ''snap back'' when throttle is opened and dropped..but slide will not fully close if cable is not fully inserted on either end. It can dislodge and reinsert easily if cable is pulled, etc etc. Seen it happen many times.(it may already be back in the proper position now) The flywheel key shearing would not cause your problem, it would be a result of your adventure...when the heavy flywheel is spinning wildly and motor is quickly stopped, sometimes the taper is not enough to hold the position and the key gets sheared off (inertia). This key holds your flywheel and ignition trigger point in the proper position to fire your spark at a precise moment, if your key shears, you will still have spark and your flywheel will still turn...just not trigger you spark at the correct time. best of luck Quote Link to comment Share on other sites More sharing options...
dakh Posted October 23, 2018 Author Report Share Posted October 23, 2018 Yes that makes a lot of sense, thanks! Now to hunt down the right flywheel puller... What can be done to prevent the throttle sleeve to pull out and get stuck? Maybe go around the joint with some tape? Quote Link to comment Share on other sites More sharing options...
misscrabstick Posted October 23, 2018 Report Share Posted October 23, 2018 I had this happen to my Beta 300, i had forgotten to turn off the fuel whilst in transport on the trailer, got home cleaned the bike started it up for a dry off and it revved it's nuts off! kill switch and plug lead off had no effect, my guess being it was igniting off the exhaust gases just leaving the cylinder as new gas came in due to the speed, it wasn't carbon glowing as it only had a few hours on it at that time, luckily no damage occured. Quote Link to comment Share on other sites More sharing options...
dakh Posted October 23, 2018 Author Report Share Posted October 23, 2018 Thinking about this, even if the throttle somehow got stuck open this would not explain it. It would not have revved past the rev limiter and would have stopped with the stop button and definitely with the plug wire pulled wouldn't it? Or it was first the throttle cable got out of line and then by virtue of it running for a few seconds like that it started to self-ignite? Turns out I probably have the right flywheel puller so should be able to test the sheared key theory pretty easily. Anyone knows what years TXT I should be looking up parts for on this 2017 Contact ES? TIA! Quote Link to comment Share on other sites More sharing options...
peterb Posted October 23, 2018 Report Share Posted October 23, 2018 From your description it seems that you stalled the motor before the piston nipped up, so likely then that there is no piston/bore damage that usually happens when the bikes land upside down and the throttle sticks wide open till engine seizure. Have a look at the throttle needle clip, and see if there is a plate on top of the needle that holds it in place, it's possible that the needle is allowed to float without any top plate, or is perhaps installed incorrectly. I have had a throttle slide with a nick on the slide surface caused by something getting through the air filter in the past, that would occasionally stick open. Bye, Peter B. Quote Link to comment Share on other sites More sharing options...
dakh Posted October 24, 2018 Author Report Share Posted October 24, 2018 (edited) It appears that maybe the bike is just flooded, or it's flooded in addition to whatever else is wrong with it. I pulled the tank off and checked the throttle cable, I can see now how the cable housing would pull out of the metal piple that goes into the top of the carb and stay perched on its edge. It may or may not have happened, but yea bad design, the piece of the pipe where the cable housing is going into is just too short/shallow to be sure it won't come out. I did the whole throttle wide open and kick it a bunch of times deal with fuel off and it backfired pretty good on me a few times. Pulled the plug and it was wet, even though it was a new one I just put in (after the runaway episode). So I'm leaving it overnight with the plug out to dry. This is my second 2-stroke, all my other bikes are 4-stroke (Honda CRFs) and the first one was a KTM 200exc that never flooded to the point of not starting like this. Edited October 24, 2018 by dakh Quote Link to comment Share on other sites More sharing options...
Jeff B Posted November 2, 2018 Report Share Posted November 2, 2018 I got to know. Did you find the problem? I have a 2017 Contact 250...non ES. It has been a flawless. Quote Link to comment Share on other sites More sharing options...
dakh Posted November 2, 2018 Author Report Share Posted November 2, 2018 3 hours ago, Jeff B said: I got to know. Did you find the problem? I have a 2017 Contact 250...non ES. It has been a flawless. I screwed around with it for a bit without opening anything up. Drained 3 charges of the battery trying to start it in various conditions, removed the spark plug a bunch of times etc. No go. It will backfire pretty good once in a while but not even trying to run. Will try to pull the flywheel this weekend and see if I snapped the key. Called the dealer though and they said flywheel moving isn't common. Maybe I just have some junk stuck in the carb that produced the initial problem to begin with. Quote Link to comment Share on other sites More sharing options...
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