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Stuck Throttle - 2005 WR450F

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I was at Shane Watts Dirt Wise class this past weekend (awesome experience), and had a 30-40MPH off when my throttle stuck open (about 1/2) during a sprint race. Rather than plow into another set of riders, I self-sacrificed and tucked the front.

 

Immediately after the incident, I jostled the throttle tube, which moved freely - no spring resistance, then suddenly it snapped back. There was no binding at the throttle tube, so I'm guessing it got hung up either internal to the cable, at the carb connection, or the internal slide.

 

I've not started diagnosing yet, but is there anything else I should consider as I dig into this? Prior to the incident, there was zero evidence of notchiness or binding in the throttle, and once it snapped back (post incident), it felt 100% normal, and I finished out the day of riding with no further issue.

 

I would like to "fix" something, though, to prevent this from happening again.

 

Thoughts?

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Didn't have your hand on the clutch?


Yeah, but I didn't react fast enough. Once I got into race mode, I left my good sense at the starting line. I have an extensive street/track riding background, so I should have known better. I literally have 6 hours experience on my first dirt bike, and I jumped in too much, too soon. I was spending most of my mental currency on proper dirt body position/technique (consciously trying to not fall back into pavement habits), and I didn't have enough processing power to deal with the issue when it arose. Classic gumby.

It was a valuable lesson, and luckily, I got out of it relatively pain/damage/cost free.

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Happened to me too, and I was one of those guys who "knew" it could never happen to me. Cost me $15,000 in knee reconstruction and 6 months off the bike, and I bet I wasn't going 30 mph when I hit the ground. :-) 

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The number one reason for this happening is binding at the bar/throttle tube/grip/handguards. Inspect and alter/ replace.

Second is a cable set that is routed incorrectly, and is kinking. cable should route on the right side of the tank, not the factory left side, and should be free to move by pulling on them.

Third is a worn out 'pull' cable or throttle housing. If it's original, it's competely worn out, so replace it. Motion Pro or OEM. Do NOT get Tusk cables.

Fourth is a very dirty carb, and the slide plate and seal are all gummed up. 

Fifth is a broken 'push' cable, and the slide is sticking up due to motor vacuum on the slide.

Edited by Krannie McKranface

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Thanks, Krannie. I replaced the bars and put hand guards on and was anal retentive about ensuring there was no throttle tube binding. I also installed rad guards and verified routings at the time. The clutch cable routing was jacked, but everything was fixed and routed per the manual.

I'll get some new cables per your and LSHD's suggestion (I assume they're original) and clean the carb as well.

Thanks again, gents.

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cable should route on the right side of the tank, not the factory left side, and should be free to move by pulling on them.


I just noticed this specific comment. In the manual, for my 05, it specifies the throttle cables run down the right side between the RH radiator and the frame. Assuming I'm reading the manual correctly, there is a weld loop near the steer head on he RH side which the clutch, throttle, and hot start cables all pass through.

Maybe throttle routings were changed on later models? I don't think my throttle cables would be long enough to route down the left side, even if I tried. :)

At any rate, you guys gave me a good list to check through. I'm going to tear into it this weekend.

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I wanted to provide a follow-up based on your feedback. I ran through the suggestions and did not find any "smoking gun(s)".

The number one reason for this happening is binding at the bar/throttle tube/grip/handguards. Inspect and alter/ replace.


Double checked this, all looked okay. Nothing under the throttle tube. No contact of grip flange with anything, no contact of throttle tube with hand guards, etc.


Second is a cable set that is routed incorrectly, and is kinking. cable should route on the right side of the tank, not the factory left side, and should be free to move by pulling on them.


Verified cable routing was per the manual (right side on 05) and no binding/kinking present).


Third is a worn out 'pull' cable or throttle housing. If it's original, it's competely worn out, so replace it. Motion Pro or OEM. Do NOT get Tusk cables.


Checked the throttle tube and housing. No abnormal wear, burrs, etc.

Replaced the cables with Motion Pro. There was no external sign of damage to the OE cable removed. I assume this was the original cable assembly (i.e. 12 years old).

On a side note, when I was looking at cables, I saw OEM cables were $45, MP were $9.50 (for the set). I then saw All Balls cables for $24, and opted for those. Surely they'd be better than $9 cables, right? Well, the cable guides on the AB cables (in the throttle housing) were 6mm narrower than OE, which caused severe binding once assembled. The grip would not return to idle when released unless forced closed. No bueno.

Returned those and got the MP cables (as originally suggested 🤦‍♂️). MP fit nicely with no problems.


Fourth is a very dirty carb, and the slide plate and seal are all gummed up. 


I pulled the carb and cleaned it thoroughly. However, other than the crust and gunk around the fuel inlet fitting, the carb was otherwise immaculate.

Zero gum around the slide, but I did find one very minor scratch on one of the outer walls where the slide wheels ride. The scratch would have dragged on the face of the slide wheels. It was deep enough I could feel it with a fingernail, but not so deep that my nail got caught. I polished out the scratch with some 600 grit sandpaper as a precautionary measure.

Replaced the slide plate seal (original looked okay). Lightly oiled the slide channels.

Installed a JD Jetting kit while I was in there, for good measure. :)

I'm guessing the PO likely cleaned the carb at some point. As there was evidence someone was in there.

Float bowl screws had some obvious witness marks from prior removal. AP linkage had an o-ring installed. YZ throttle stop screw installed. Jetting appeared to be stock.

I pulled the throttle stop screw and measured it against the YZ screw I purchased, and they were exactly the same. It looked like the screw was an actual YZ screw and not a cut-off OE screw.


Fifth is a broken 'push' cable, and the slide is sticking up due to motor vacuum on the slide.


Replaced with the pull cable, since cables came as a set.

I'll monitor performance for now and check back if I continue to have any issues.

Thanks!
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