I went for a good rip on the 250 this afternoon. About 1 hour in I lost traction near the top of a 20 footish very steep hill and had to jump. I skidded down on my head but luckily the bike didn't hit me, and very lucky - zero damage - but that's not the lucky part.
I cleared off the mud and kept riding. I was riding on some tangly rocky hills, steep and technical with lots of vertical dropoffs, and I was doing some fast 6th gear wheelies, nice and steady. Then for the first time this year (the snow is just melting) I ran up a very very steep sheer rock face. It was just below freezing today so the tire wasn't super sticky, so it was a real good challenge for me. I ran up and down 20 times or so with a bit of spinning here and there but no tumbles.

I knew I was getting low on fuel so I headed back towards home, again 6th gears wheelies on the return trip down the level stretch. About a mile from home I ran out of fuel, but I had a liter with me so I poured it, but that's not the lucky part. I fired up and was cruising along parallel to the street just before mine, in the rough. There's a nice little 2 foot high near vertical rock that I ride over on every trip, and I blipped the throttle to shoot over it. That's when bad things started to happen. It was like someone had remote control of my throttle and pinned it. I shot up that rock like never before and came off the pegs but held the bars, and the bike swung straight out in my hands and I landed on my knees and the bike landed upside down, me still hanging on to the bars. The engine was pinned and spinning in 3rd gear, and my killswitch doesn't work, so I twisted the bike on it's side and jammed on the rear brake and stalled it. Where I landed was soft and mossy so again, looked like no damage. The throttle barrel was loose, and the cable obviously stuck - but not much - maybe 1/4 throttle - no where near what it it should have taken for that launch. I pulled on the cable at the carb and got it back to normal, and decided that maybe it  was stuck at WFO and then backed off to 1/4 when it was dancing on the ground.

I started the engine - perfect - tested the throttle - perfect, nice and free so off I went the last 1/4 mile to home. I didn't trust the throttle and thought I must have damaged it during the crash earlier and maybe a broken piece just decided to jam, so I was just putting along in 3rd, basically just above idle. I came to a small hill that needed a very small tap of gas, so I lightly tapped it, and I was back in rocket launch mode. Although the throttle was barely turned, the engine was WFO. I grabbed the clutch, got the front down, stood on the rear brake, and popped the clutch and killed the engine. Again the throttle barrel was loose, like the cable was stuck, but I'd say less than 1/4 turn. I stretched the cable again, got it back to normal, and decided to drive the last little stretch on the paved road to avoid blipping the throttle in nasty rocky patches. I fired up again, perfectly normal, snapped the throttle several times, perfectly normal, and then I rolled through the shallow ditch to get up onto the road. I gave it a tiny pop of gas to get up the side of the ditch and was right back to full afterburner. I wheelie right out on to the road, luckily no cars were coming, and came off the pegs as the bike flipped backwards. I grabbed the clutch and ran behind it and managed to get it down on 2 wheels again, but I still had the clutch in and the engine was seriously screaming like I've never heard it scream before, and I'm in the middle of the road. I jump back on the bike, plant my heel on the rear brake lever, and let the clutch out to try to stall the engine, but the clutch wouldn't hook up, it just slipped. Engine still screaming, in the middle of the road, no way to shut down - I decided to try to pop the clutch with the brake locked to stall it - bad idea.

The bike launched right out from under me and ripped the bars out of my hands, and actually seemed to shoot into the air a little bit, and it was nearly vertical when the spinning rear tire touched down, and then things got really out of control and I can't say for sure exactly what happened. The bike bounced and bucked a bit as the tire touched down now and then, and it was moving roughly forward cause I was jumping down the road trying to get a handle on it. It was a crazy scene - completely out of control, engine screaming, plastic and lever shrapnel flying around, and still in the middle of the road. It finally settled down on it's left side and was spinning in circles, and looked tame enough to grab, so I caught the bars, pulled in the clutch, jammed the rear brake and popped the clutch and stalled the engine, still lying on it's side in the road. The rear fender shattered from the cold and there was plastic and white skid marks all over the road. I'm sure if anyone came along they would assume that I flipped doing a wheelie, so I decided to skip the cleanup and get the heck outta there. I pushed the bike the rest of the way home, the fender dragging along by the wire, and just parked it and sat here to write what happened.

Although the throttle cable was sticking, it can't be responsible for the power output that I experienced. Honestly, I have never felt that kind of power from my bike. So - I'm thinking either a crank seal popped and was sucking in air, or I mistakenly had straight gas in the 1 liter bottle, or both. Anybody ever experience anything like this?

If this had happened during the high speed wheelies I would have had some nasty road rash, and if it had happened on that rock face I would have been in big trouble. I cannot believe how lucky I am that this happened where it did, Jaysus!

Lazer - I need another rear fender (airbox is OK) and another pair of grips, aaaaaaaand a throttle cable, and DEFINITELY a kill switch. Strangely, I have never broken a lever before so I still have my original sets of spares. :-)

Cheers

Frosty

Edited by Frostbite, 27 May 2012 - 06:59 PM.

Hey, Frostbite!!!

Maybe you should change you username to "Mr. Lucky", or something like that......   

Now, while it could be a lean condition causing something like you describe, since there was an "accident" I'd be certain to check the possibility of your throttle cable getting a bunch of slack in it, or a kink, and possibly being able to come out of the adjuster/guide thingy, at either the throttle assy., or down at the carb. What I mean is this: The outer cable can "jump" out of it's little adjuster/guide dealies on either end if things get too slack, and that can cause a stuck throttle situation. Mud & crud in your throttle housing on the bars can work randon mayhem, and if you went down in some slop, that's a good place to look at & clean. Check throttle cable for kinks. KTM 2-strokes had the problem of sticking throttles when the cable got too much slack in it. Guys would run a lot of slack to beat the problem of "whiskey throttlle" that you get when you get tired late into a race (or early in any race, if you're like me....   ). The outer part of the throttle cable then would come out of the brass adjuster on top of the Keihin PWK carb, and cause a stuck throttle situation. One fix was to safety wire the outer cable housing down to the adjuster, so it would stay where it was supposed to. It still allowed a little extra slack, if a person still wasn't scared enough after that......


I wouldn't rule out your lean condition/crank seal theory. but I'd certainly check everything that has anything to do with your throttle control, from the bar to carb, first. I have had engines sorta "run away" as they were running very low on fuel. My chainsaw does this regularly. If you were in a long wheely, sometimes, with a tank low on fuel, you can get a lean condition that way, due to the angle your carb is now at while in a wheely. This is very much "if", or "possibly" kinda stuff. For trouble shooting, I like to go with a question like "What changed to keep things from working normally?". And then I'd check my throttle cable, housing, and stuff like that, first......

Hope this helps ya some!
And I have to say, I admire the heck out of a guy that rides when & where you do, Frostbite!     

Jimmie

Added in EDIT: Frostbite, what kinda bike do you have? Isn't it a Gas Gas? I haven't owned my 280 Pro TxT very long, but there's been a couple of times I either was in a lower gear than I thought I was in, or I got sloppy with my throttle. Mine seemed to take off like I'd just filled it fulla Rocket Fuel or something, giving me a case of "Big Eyes"   and a death grip on the bars.   I wonder if this possibly might not be a "Gas Gas" thing? I've heard folks say the 280s, and sometimes the 300s, can really be random little jets at times......

Edited by Mr. Neutron, 27 May 2012 - 07:38 PM.

Hey Neutron

It is a Gasgas, I have 3 250's, and have put hundreds of hours on them and this has never happened. I know what you mean about some 2 strokes revving when they run out of gas, but I run my GG's out every ride and they simply bog and die.
The first flip I blamed on the throttle probably being damaged in the crash, but the fact that it seemed to be WFO when the throttle was only turned a small amount makes me think there is something else going on. I'll pop another cable and barrel on and test it out.

Glad to hear your OK. WOW! Forget the mechanical's  - I think you better take your bike to a Shaman and have it cleansed of evil spirits...

Im with Mr. Neutron on the cable/mechanical theory for starters and have never known a GG crank seal to need replacing. Given the temp extremes you ride in - you may be in uncharted territory. (but your used to that where you are)

If you feel it's related to an air leak - I would check the intake manifold 1st. The cold and vibration may have cracked it.

The only similar ghost revving experience I have is that, under light loads, the revs will build to high levels even under partial throttle - but they tend to ramp up relatively slowly. They will go very high if your past say a quarter throttle.

Being the McGyver of the tundra, I'm confident you will solve the problem quickly. But in case you dont, please do us all a favor and next time you test the bike, do it in front of your camera...I will pay money to watch you wrestle that thing.. I really think we need to call discovery channel and get you on the TV!

Edited by laser17, 28 May 2012 - 04:42 AM.

Hi Laser

What do you think of the straight gas possibility? None of it makes much sense to me because it was intermittent, so not likely to be the gas, but the power was crazy when it would run away, and I was barely opening the throttle. Honestly, the first time it happened up that little rock face was a real eye opener to me. I have never cut it loose like that before, but now I can see how guys can shoot up some serious ledges. I'm sure I was a couple of feet in the air above the top of the rock, and I rolled up to it at a few mph, it really exploded up the face. Of course it could also be that I wasn't expecting the big power hit, so maybe it only seemed stronger, and I tend to shut down at the top of a ledge, not stay WFO right over the crest. I think I caught a glimpse of  the capability of the bike that I haven't come close to tapping into yet. Ever see the ghost rider technique used in enduros like Last Man Standing? That's what my bike did on it's own in the middle of the road, completely launched without me, pretty amazing to experience that, haha!

As for the Disco channel, been there.......  

I dont think straight gas would do that - heck it would technically be richer! I have never tested the theory though...My money is on the cable/carb/throttle side of things. In that dense air of yours, I imagine the 250 has some serious power up top. Mine never gets past about 5K rpm....

I forgot about the discovery channel episode! That's awesome.

FWIW: Dont forget to check the outer throttle cable sheathing getting pinched against the frame and tank as well. Doesn't account for your exact experience, but is a common problem. Given you had just done "something" with the tank - could be tank related this way. (I know its a stretch - but what the heck.)

My money is on the cable or cable sheath jumping out of it's home.  With any additional slack like you experienced after the crash, it's a good sign that there is a potential for something to hang up.

1/4 throttle doesn't sound like much, but in riding, you'll very rarely use that much. And with no real load on the engine, it will quickly rev to the limit at 1/4.  Now, is that 25% throttle or 1/4 turn?  On most regular throttle tubes, 1/4 turn is about full throttle.

If you haven't already, see if you can get it to do it while NOT riding it, like standing beside it in a tall gear with clutch pulled in, bounce the front to shake the cable and turn the bars and stuff like that..  But probably a better idea is to play around with the cable (with the engine OFF) by  pulling on the sheath slowly and see if you can feel any slack at the carb top AND / OR at the throttle end.  there should be NONE.  There should be a very small amount of slack in the cable itself, but very small..  I ALWAYS listen carefully at the carb every time I do anything with the throttle, carb or cable for that "clunk" sound as the slide bottoms out before I start the bke.

I wouldn't rule out an ice problem with ice building above the slide and then sticking the slide open when you pull the slide above to that spot..   Something like that frozen piston problem you had with frost in the cylinder.

Also, even with a good kill switch, a 2-stroke revved out will continue to run WITHOUT spark if it revs high enough for even a couple seconds as it acts like a diesel engine.

Running lean as in fuel starvation should NOT produce that much power if the throttle is working correctly....   Again, my money is on something to do with the sloppy cable and / or ice or frost sticking the slide.

Happy to hear you survived... sorry about the bike..   I was gone all weekend helping Shaun (You remember and rode with Shaun).  He bought 131 acres of land on a super steep hillside in Eastern WA and we have started building the first of many trail systems...   No ice here!  

Edited by 2PLY, 29 May 2012 - 09:46 AM.

I had another thought about the ice.  You said you added a bottle of fuel before this happened?  Possible water contamination with ethanol combining with the water and then forming carburetor ice UNDER the slide. It could form instantly, just enough to prevent the slide from returning home.  And then it would melt instantly once you stopped the bike.

2PLY, on 30 May 2012 - 07:31 AM, said:

Hi Curt, I was away and just got back, so I'll check the bike. It was 25% throttle, and it stuck with the bike sitting still. I'm honestly surprised by the power that was generated, especially at such a small throttle opening. I won't know if it was ice, we actually climbed above freezing today! :-)

2PLY, on 29 May 2012 - 09:44 AM, said:

Sounds like it's time for me to head southwest! :-)

Frostbite, on 04 June 2012 - 08:23 AM, said:

Funny...   I just sent you an email question about this and then came back to the TT page...  But YES, come for another visit if you dare.  We are just in the starting phases of opening up his land, but it appears we could be there many years developing it.

But somehow, we HAVE to meet in Utah for a ride on the 5 Miles of Hell  (Heaven) trail. Will have to arrange for a bike for you unless my 04 300 would do....   OR, YOU ride the 07 Raga and I'll ride the 04.

About the throttle....   I was thinking ice in the carburetor slide, possible water contamination mixing with the Ethanol they use in gas these days to explain why it happened after adding the extra fuel.  And then, the possibility that a small amount of water in the throttle cable could be freezing and sticking the cable when you open it much past idle..   

I know Stu said the ICE in the throttle cable has happened to him before.

laser17, on 04 June 2012 - 09:19 AM, said:

It used to happen to me all the time in my old VW Bus when coming back from a day snow skiing. I had to be careful to test the throttle before applying gas or it could be stuck at a 4K RPM Idle !!

Before I replaced the cable and sealed the ends of the cable tube, I would have to start the engine carefully, wait for it to warm up a little so that I could maneuver at idle speed so that I could turn the rear of the Bus into whatever breeze there was so that the heat of the engine would waft across the cable and thaw it...  Otherwise, it was lay down in the snow with a torch to thaw the ice in the throttle cable tube  YUK!!!

So far, has not happened to my Syncro... (crossing fingers...  knocking on wood)

  Hmmmm. Another good arguement for "Fly-By-Wire", I reckon.....

Jimmie

So, the plot thickens. I took the bike apart tonight. Throttle barrel was fine with a tiny bit of dust in the little part that changes the cable direction 90 degrees.
I drained the gas from the carb, normal.
Removed the float bowl - clean inside
Checked everything, throttle cable moves freely - BUT - I had removed the tank to have clear access to the cable, so now I'm thinking the cable got pinched under the tank.
I see the black box is floating around - the rubber strap that holds in in place under the tank near the steering head is broken, so it may have floated around and pinched the cable.
Everything seems fine now so I try to start but nothing. I pop a new plug in and check for spark - nothing.
Check all electrical connections - OK
My 08 used to hold water in the flywheel cover and that sometimes killed the spark, so I pop the flywheel cover. I see a scratch on the flywheel where the pickup is positioned. I start to rotate the flywheel by hand, and it wobbles. The bolt is loose and the key has sheared off.
Sooooooo, for the experts - what came first - the chicken or the egg - do you think the key sheared when I locked up the engine to stall it from WFO, or do you think the loose flywheel changing the ignition timing, combined with a slightly sticky throttle could have accounted for the turbo boost I experienced?

Edited by Frostbite, 05 June 2012 - 04:35 PM.

I think a loose FW sheared the key when you stalled it and most likely resulted in the damaged pickup  - but who knows what happened while on the way out of time. Pinching the cable against the tank is common and you did muck with the tank prior to launch, but I still wouldn't bet my life on it given the environmental aspects of what you see. So im all in with a definitive.. could be...

Fixing the key and pickup while also ensuring smooth throttle cable operation would seem like the place to start.

Good luck
T

PS - you missed a great trials! Rained close to 2" the day before so was a bit slick and nasty. All that practice on the ice would have come in handy.

This sounds more like a loose carb. I have seen situations where the carb sorta comes off and the result is virtual full throttle. Nothing else I can think of does what you describe.

For Gawd's sake man, fix you kill switch!!!

As for your problem, I'm calling occasional sticky cable outer and massive air leak - I like the sound of Dan's loose carb.

Flywheel sheared as a result of the violent stalling.

This used to happen on my 300Pro from time to time. But I had a functioning kill switch. It taught me to keep the clutch covered at all times! Then it happened with a friend riding and launched him into the back of my Ford Expedition. He was in the hospital for a week. Got rid of that bike! Bought a Montesa Cota 315R and haven't had any more problems like that.