YZ426F Won't Wheelie

No because I've wheelied the bike before so I know where it needs to be as far as speed. Ive picked it up in 1st 2nd and 3rd. Grayracer is definitely right about it not being a clutch slipping. If it was the clutch slipping it wouldnt keep going back into 5th when pinned. (Its a jolting sensation) I'm going to crack the case but I'd bet money I'm going to find a bent and scraped shift fork and gears with the dogs rounded off.

A slipping clutch and a gear "popping out" are very different in how they feel on the bike. A clutch is a friction device, same as a tire is, and will hold to varying degrees. Usually, it will slip worse in the higher gears because the load on the clutch is greater in those gears by reason of simple leverage. But the outward effect will usually be evident in the top 2 or three gears (worst in 5th), rather than just one gear, and except for the fact that the rear of the bike won't slither around, it will sound and feel somewhat like the rear tire loosing traction.

Gears jumping out of engagement are another matter. They are designed so that the locking lugs on the side of one gear lock into the lugs or slots on the gear next to them, holding the free gear to the shaft and making it the operative ratio. The lugs are originally built with a slight undercut so that the driving load actually pulls them together, but over time, they can wear to the point that the undercut is reversed, and the load pushes them apart instead. When this happens in a car transmission, the gear is able to move the shift fork to the neutral position, and the trans jumps all the way out of gear with a bang. But in a bike trans, the cam that moves the fork cannot be rotated by this kind of force, so instead of popping free and staying there, the thrust bends the fork until the lugs disengage, at which point the drive load is relieved, and the gears rotate until the lugs align again. Once aligned, the deflected fork slams them back together. If the power is maintained, the cycle repeats, and you end up with a repetitive harsh jerking under power.

The other giveaway is that this will be confined to happening only when the affected gear is in use, and not at any other time.

i had a hard time wheeling with my yzf 450 , turn out the clutch plates were slipping

Thats would be nice if its my clutch plates stopping it..i have a whole kit coming monday..

Is there a trick to getting the magneto off?

Use a flywheel puller

Use a flywheel puller

Or make your own. I made one with a crescent wrench and 2 bolts.

crescent_wrench_2.jpg

Touche, that is pretty cool. But the puller is only like 10 bucks

It sounds to me like this bike has been violated. Leaving a multitude of reasons of why it doesn't apparently have enough power to wheelie. Is the top-end shot ? Cams out of time? Who knows? ...... If the previous owner couldn't assemble the carb correctly then it's possible (and likely) he violated the rest of the bike as well.....

Tear the engine apart and find out.......

Just my 2 cents...

I have the top end off already. Everything is looking good so far but I dont have any of these special tools. I can get the flywheel puller for the cdi magneto but is there any others tools that I will have to get?

I have a 2002 YZ426F I am 300 lbs I sit close up to the gas tank and still the bike pulls the front wheel up in 1st 2nd and a little in 3rd I will have to say my bike is one beast

Hey guys,

Just wanted to give everyone an update. I've slowly been rebuilding my bike over the past couple weeks. Everything has been going pretty well. All the transmission work is complete. (Put the 3rd/5th gear pinions in and replaced the center shift fork) It was very obvious that the shift fork was worn out because it has a huge gash in it. When comparing the new pinions I could see that they were worn down also. I will make a final post next week when the bike is together and running. This is my first rebuild I've ever done so if any people reading this are doubting themselves dont worry just go for it. It's not worth the amount of money they would charge at a shop.

Thanks for all your help! :smirk:

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