Revs from hell -- stuck throttle or bad mojo?

[AZRickD]

I was having a ball on my 2005 EC250 at this weekend's race. A 52 mile GP north of Tucson. Rocks and sand. Nothing particularly technical except for lots of ingress and egress from silty sand washes.

I was on my second of two laps with five mile to go when I exited some single track and came to a kinda fun, long, rocky jeep road with a modest incline. I was motoring up nicely when I noticed (the whole thing transpired over a period of about 4 seconds -- or less) my revs begin to build, slowly at first, then faster. Like a Cox model airplane that had just run out of fuel. Lean condition.

I was well aware that I hadn't changed throttle position and was wondering about a stuck throttle. But this "stuck throttle" resulted in more and more revs until it was screaming beyond the point that my front tire started to loft (pre-loop).

I _attempted_ to grab a fist full of clutch and brake but I kept moving as I tried to find the kill switch and lost some leverage on the clutch lever. Moments from disaster (heading to a rock pile), I decided to do a strategic dismount and fix things later. As I dropped the bike I slammed my pinky into a rock (broken finger, rock is doing well). The sweep and course worker heard my still screaming motor and rushed to my aid as I finally found the kill switch on my now looped and pointing-downward bike (musta looped it when I let go of the clutch).

I re-started it and it was still acting funny. I couldn't tell if my throttle was sticky or if my hand was numb. I rode it up to the top of the hill with it still acting strange. It was revving mid-high, but not like a banshee as before. The sweep told me to shut it down. He said he was going to find a short cut for me but I told him I'd finish. With no real solution in sight, I backed off the idle screw and re-started. It behaved normally but I doubt the idle screw had anything to do with it.

I rode at sub RickSpeed with no real problem accept for the double whoop section and some particularly rocky sections flexing my stiff-as-a-board pinky. I was spooked that I might tip in a wash and prang my finger but that didn't happen. I did get my pinky thwacked by three tree branches though. Glad I had big bark busters on.

Not sure what happened to my revs. Stuck throttle or stuck slide doesn't quite answer it since the revs slowly increased to the moon without any grip input from me. *New thought* I wonder -- maybe the float got stuck partially closed and caused the carb to go lean.

I'll be at the doc's tomorrow getting x-rayed and set.

Typing with one hand sucks.

Thoughts?

Rick

[Bearman]

You know where the throttle cable enters the the throttle body on the handle bars? Does yours have a little cap-like thing that you can slide on and off? Ill get a picture of it if you dont know what Im talking about. Anyway, I find that mine occasionally slides off and catches, causing the throttle to twist and the bike to rev harder.

I'd check this out, seems really simple, but it catches me out often

[Rick]

Safety Wire The cable to the throttle and the same on the carb...cheap insurance.....if the cable came out of the housing...

[AZRickD]

This was already safety wired. I'm almost certain this area of the system had nothing to do with the problem I experienced.

[Rick]

Sorry to hear about the pinky finger, broke my right one also on a bad get off a few years back..Was out at Moonrocks, NV, anyway, I think I'd pull the filter and see if there is any dust or very small grains of sand they may have somehow got by the filter and into the air boot to the carb.

Check your airbox to carb boot to make sure it did not "come loose" or "slip off", which have caused a grain of sand to get in a jam the slide.

With airbox off and the carb bell expossed, if there was any dust that may have by passed the filter you should be able to tell due to a little premix being on the carb bell and a tell tell sign of dust, ect.

Check your throttle cable for SMOOTH opertion.

Did you fall prior to the this happening? If so, then maybe some dirt worked it's way into the throttle tube between the bar.

Pull you spark plug...have a look there and see how it is burning.

I know I'd go over the entire fuel system from craddle to grave, throttle cable/ throttle tube / cable routing / carb mounting / carb vent hoses / airbox boot clamps and filter. I also would pull the carb apart and check the slide and that plastic part that hold the needle in place and spring.

Good luck hope you figure it out. Please keep us updated on your findings.

[AZRickD]

While I will do all that (when my pinky allows), those item don't explain the behavior. Without any input from me, the bike began to build revs. Then, a few minutes later, all was well.

Sand in the boot wouldn't match up with that.

[LAWMAN]

sand in the fuel could cause it to rev up from running lean, then it could have worked itself out.

might have been an air leak, but I've never heard of a self-curing air leak.

[fury1]

had a similar incident,racing in NY dusty conditions,cruising in third gear having a great ride,throttle just started revving up on its own,killed it and loosened the clamps and spun the carb and pulled out the slide,as my row went by looked ok in there,didnt see anything too bad,but put it back together and it never happened again,Im thinking a little dirt got in mine and jammed the slide,I also had the throttle stick once and changed out the cable to a longer one,one full throttle experiance was enough!

[AZRickD]

Fury,

Dusty? Very !!

I've been going through the bike replacing this and that over the last few weeks. I've always thought my throttle cable was too short. Time to Call GoFasters.

Got my pinky set today. The magic of novacaine.

[ramcclure200]

Sounds sort of like when you kick start a 2stroke and with out throttle input it just starts revvving to the moon and puts you in a frantic effort to hit the kill switch.
I don't know what causes it to do that, air leak, stuck slide?
Ron

04 ECDE200