Unexpected High Rev / Acceleration

Hey folks.

I have a 99 YZ 250 that I purchased about 2 months ago. I hadn't had a bike for about 10 years and boy I missed riding. I'm 34 and I don't go crazy or anything. I rip around sometimes, but I know my limitations and skill set and thus I keep it in check. lol

Here's the deal... Sunday I went for a quick ride on some trails for about an hour before I headed back home to do the family thing. I was riding pretty easy, and most the trails were 1st or 2nd gear 90% of the time. On the way back into the trails I had to go across a real sandy area that had a bunch of whoops in it. I got on it a little to stay up on top the sand and for whatever reason the throttle took off on me. It wound up and just started taking off like a rocket. I got the throttle rolled forward and luckilly for me I was in a wide open space. It went back to normal and I chalked it up to a freak deal. I rode for about 30 more mins just riding trails and not shredding around or anything. Just enjoying the day....

Then, I was back in tight trails.... I had a couple small whoops coming up and a short straight-away. I turned the corner and "Brrraaap" on the trottle a bit and she wound like a SOB and took off! I didn't even have time to say "OH SHEET" - I was positioned myself on my bike to hit the whoops and clutched, braked and tried to whoa this runaway rocketship.... The last thing I remember was the front end washing out and starting over the bars. I stuck my hands out and thats the last thing I remember.

The last thing until I woke with 4 riders that came across me and rendered to my aid. I have no idea how long I was out. How long until they found me, or anything else for that matter. They called EMS and they came and took me out. I didn't realize how banged up I was.

I got some pretty bad lascerations, broken bones in my face, and I had to reschedule my Glamour Shots for awhile. haha... No, I wasn't wearing a helmet and Yes I know even though I wasn't shredding or roosting around I should have had one. But, subsequently I didn't...

What on earth could have caused it to do this?

Your input on the problem would be much appreciated.


That's a typical 250 MX smoker for ya. They have that big hit when you get on it.

I appreciate the reply but I disagree. It wasn't "Coming on the pipe" it freaking revved up wide open on its own voliton.

Did it rev up on its own or did the throttle stick when you tried to back off?

sounds like your throttle cable is not routed correctly, and when you turn sometimes it pulls the cable up and you eccellerate. Take your tank off and check if the cable gets tight when you turn the bars. Also make sure your throttle grip assy. is as far to left to give cable as much slack as possible.


Kinda both... The best way I can explain it is that I burped the throttle, once I was off which was like a split second it revved rapping up and accelerating high and fast. I had a second to try and do something. I remember clutching, braking, and rolling my wrist forward on the twist throttle. To late...

It clearly surprised the heck outa me. I wasn't gassin it up. It wasn't like it came into the powerband hard and I wasn't used to it or something. It rapped up and took off. I just remember thinking... "This isn't a good spot for this..." lol

The bike is fine. I will heal eventually. Although, it makes me REALLY skittish about swinging a leg over it till I know we ain't having that issue again. EVER.

Edited by EPbirddog

You rode for an hour with no helmet? Like the saying goes " if you gonna be stupid you better be tough ". Sorry to hear that but I would disassemble everything from your throttle to and including your carb. Inspect, clean, and lube everything. I would pull the tank and check cable routing and if it was me, replace the cable just in case. A runaway is a scary ass feeling. Hope you get well soon!


Maybe made it 30 mins. I had planned to ride about an hour. I probably got my hour in counting the ambulance ride. lol

Almost sounds to me like you are experiencing "whiskey throttle". You get in a funny position, kind of fall back, causes you to pull the throttle open more, and bad things happen in a hurry.

If the bike truely is staying throttled up on it's own then it should be fairly easy to find the culprit somewhere within the throttle/cable/carb.

And why the F would you ride without a helmet?

And why the F would you ride without a helmet?

I had one back when I had my old bike. It got "Borrowed" and never returned. I should have replaced it, but I didn't. No excuse.

No worries... I'll have plenty of time to shop for one while I wait for my orbital bones, and the ginormous lascerations to heal on my face. But thanks for bringing it up again.

Broken throttle cable outer casing can cause the same issue

Thanks Smoke.

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