03 yz450 wants to jump in to gear

Something I noticed at the end of the season with my bike, as I would rev in neutral, when warming it up or waiting for my son, it seemed to want to jump in to gear. Had to rev with the clutch engaged after it did jump once.

Doesn't seem like a normal thing to do.

Something I should look at this winter?

Had the bike for a year now. No issues running trails other than what was noted.



I have no real clear idea what you're trying to say. For one thing, the clutch is engaged when you let the lever out, and disengaged or released when you pull the lever in.

So, what? It jumps into gear on it's own?

To clarify, it wants to jump on its own. I have started using the clutch as a just in case.

Hope this is clearer.


Hope this is clearer.

Nope, sorry.
Nope, sorry.

Pretty sure what hes saying is when he starts the bike and revs it freely with the clutch engaged, the bike will pop into gear, then goes on to say he starts it in neutral with the clutch pulled in as a safety precaution, just in case the the the bike pops in gear.

I expect you to understand normal, everyday English haha just kidding.

haha oops

I expect you to understand normal, everyday English

What has become "everyday English" is, unfortunately, not always intelligible.

What I gather from re-reading what the OP said, guessing a bit, and of course, your invaluable assistance, is that when the bike is supposedly in neutral, it will sometimes lurch forward. He does not say to what degree this happens, specifically, does it actually drop into gear and kill the engine, then remaining in gear until shifted back to neutral, or does it kind of grab, lurch forward, and release again? Is there a grinding or clashing noise associated with this?

Without further details, here's what comes to mind:

  • It's not really in neutral when it does this, but between two other gears, allowing it to fall into gear for lack of any index to hold the shift cam.
  • It is in neutral between 1st and 2nd, but there is a problem with the shift cam indexing lever ("stopper lever") that prevents it from holding the cam properly.
  • A shift fork is so badly bent that it allows contact between two gears while in neutral.
  • One of the free gears in the trans is trying to seize to its shaft intermittently.

Sorry for the ambiguity. Was doing too many things at once.

With the bike in neutral, no clutch it has jumped in to gear and stalled, remained in gear. This was while revving. It is ok at idle.

Prior to doing this, was a sound that was similar to clashing, gear teeth getting close to engaging.

As you mentioned a bent shift fork, could that account for difficulty of the gear shift lever returning to center position? Noted a couple of times but just for 4th gear.

Possibly. Check the things I listed, and also look at how well the lever on the inside end of the shift shaft centers on the shift pawl assembly. A bent lever, bent centering pin, or bent/broken centering spring may be at fault, too.

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