My 2001 Yz426 wont run right, please help


23 replies to this topic
  • Bansheeboy914

Posted February 12, 2012 - 12:47 PM

#1

I bought a 2001 yz426 that has been extremely well taken care of since it was new. The problem I am having, is that when it's in 4th gear under a load (even a small load like cruising down the street), and at the very top of 5th it has a strange miss. Almost like the motor completely cuts out and then comes back and repeats. We thought it was something in the gearbox, so we split the cases and tore it all the way down and inspected the gears, and they all appear to be in great shape. Also, there is absolutely no sound associated with this cut out, and 1st 2nd and 3rd pull perfectly.

Im driving myself crazy trying to figure this out, and Im supposed to take it to Glamis for President's Day. Someone please help me.

Edited by Bansheeboy914, February 12, 2012 - 12:48 PM.


  • Bansheeboy914

Posted February 12, 2012 - 05:28 PM

#2

Update, Ive tried unplugging the neutral switch, unplugging the tp sensor on the side of my carb, completely removed my e-line lighting coil, removing the resistor from the spark plug wire, and pulling the coil and cleaning all the mounting points and the connection for the small wire on the bottom. When I ride it, 1st-3rd cruise and accelerate perfectly. 4th, if I am literally just cruising, barely have the throttle open enough to keep it running, it runs fine, but as soon as I go to accelerate, as soon as I open the throttle, it starts to miss and skip. 5th seems to be fine, even when I try to accelerate, but I cannot get to the top of 5th in the short distance I have here to work with.

  • Bansheeboy914

Posted February 14, 2012 - 01:10 PM

#3

Anyone?

  • gscx

Posted February 14, 2012 - 01:12 PM

#4

The dogs on the gears were straight and not rounded off?

  • Bansheeboy914

Posted February 14, 2012 - 01:16 PM

#5

Yeah, all the teeth on all the gears looked great. It feels like an electrical issue, like the power just cuts out and comes back, but it seems odd that it would only be when I accelerate in 4th

  • grayracer513

Posted February 14, 2012 - 01:26 PM

#6

Yeah, all the teeth on all the gears looked great.


Not the teeth, the locking lugs on the sides of the gears. It's likely that what's going on is that the lugs have lost their undercut and the transmission is forcing itself out of 4th under a load. Since the fork can't actually be moved, it slams the gears back into engagement as soon as the load is relieved by jumping out. 3rd, 4th,and 5th gears on the main shaft and the #2 shift fork are most probably damaged.

  • Bansheeboy914

Posted February 14, 2012 - 01:30 PM

#7

Not the teeth, the locking lugs on the sides of the gears. It's likely that what's going on is that the lugs have lost their undercut and the transmission is forcing itself out of 4th under a load. Since the fork can't actually be moved, it slams the gears back into engagement as soon as the load is relieved by jumping out. 3rd, 4th,and 5th gears on the main shaft and the #2 shift fork are most probably damaged.

Would there be some sort of mechanical sound involved when this happens? I can't hear anything at all, which led me to believe it was electrical. Also, I have not noticed any problem at all in 3rd, but I did notice some wear on the shift fork when I had it apart, but did not think that was it.

  • Bansheeboy914

Posted February 14, 2012 - 01:35 PM

#8

Not the teeth, the locking lugs on the sides of the gears. It's likely that what's going on is that the lugs have lost their undercut and the transmission is forcing itself out of 4th under a load. Since the fork can't actually be moved, it slams the gears back into engagement as soon as the load is relieved by jumping out. 3rd, 4th,and 5th gears on the main shaft and the #2 shift fork are most probably damaged.

Thank you for the help, I was really hoping I wouldn't have to tear it back down again, but this is the most helpful answer I've received yet.

  • Bansheeboy914

Posted February 14, 2012 - 02:09 PM

#9

If this is the case, is there a way to fix them? Or am I going to have to buy new gears?

  • grayracer513

Posted February 14, 2012 - 04:32 PM

#10

If this is the case, is there a way to fix them? Or am I going to have to buy new gears?


Can't be fixed. The gears and fork will need to be replaced. Fortunately, they aren't terribly expensive.

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  • grayracer513

Posted February 14, 2012 - 04:36 PM

#11

Would there be some sort of mechanical sound involved when this happens? I can't hear anything at all, which led me to believe it was electrical. Also, I have not noticed any problem at all in 3rd, but I did notice some wear on the shift fork when I had it apart, but did not think that was it.

Not much noise is created by this except a physical jerking and the sound the engine makes during the skip itself, which has the sound of a misfire, sort of. The third gear on the main shaft is the one that slides back and forth to engage 4th and 5th. It's involved with skip out problems in those two gears, but has nothing to do with how well the trans works in third gear.

  • Spartan426

Posted February 16, 2012 - 03:42 AM

#12

Sounds like you have the same problem i did. Accept mine was when I was in 3rd gear, it slips out of gear, revs high and you let off the throttle and it re-engauges the engine. It's exactly what Gray said. My "dogs" were worn and literally chipped on one of the gears it was my "3rd pinion" gear. So my saguestion is to go back an dlook at them as well. because my "teeth" looked great on the gears, but my dogs were completely rounded and one was chipped.

Saguestion!: When you go to look at your gear and find wich one has the worn "Dog" then not only look at that one, BUT also the one it MESHES with! on mine the 3rd pinion was rounded and chipped, and the one it connected to "by" the "dog" teeth was a tad worn but accetple. Just a saguestion because yours might be worse then mine was. (I have a 2002 YZ426)

Hope this helps! Good luck!


[color=#ff0000]First and Second picture is of my damaged gear with the chipped "dog" the THIRD picture is of my new gear and what the dogs are "saposed" to look like.

Posted Image
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Posted ImagePosted Image

Edited by Spartan426, February 16, 2012 - 03:49 AM.


  • Bansheeboy914

Posted February 16, 2012 - 10:34 AM

#13

This weekend I'll be testing to see if when I hold the shifter up into 4th, it tries to kick back out. The pictures were great thanks, Ill definitely use those for reference if I tear it back down again. The only thing that makes me question it, is the bike doesnt rev up when it cuts out, I would imagine that if it were slipping out of gear, it would rev like yours did, but it completely cuts out, like all the power to the motor is gone.

Thank you

  • grayracer513

Posted February 16, 2012 - 11:04 AM

#14

Because of the way the drum cam shifting works, holding the lever up won't help it stay in gear, and the trans won't kick the lever back. In a car trans, the fork is moved by a pivoting lever or on a sliding rail operated by a lever, either of which can be pushed back to an out of gear position by the gears self ejecting. This is not true of cam shifting where the fork is moved by a grooved track in the cam, which the gears cannot drive backward by forcing away from each other. It's only by physically bending/flexing the for itself that they are able to disconnect, and that's also why the slam directly back to being engaged again once the load is off instead of just jumping out and staying out as a car would.

But you might get some feedback through the lever in the form of a vibration or thumping feel.

  • Bansheeboy914

Posted February 16, 2012 - 01:38 PM

#15

If it were forcing itself out of gear under a load would it rev like spartan426 said? Also would it only go back into gear if I let off? Because it's doing it continuously while I'm on the throttle and not revving at all

  • grayracer513

Posted February 16, 2012 - 02:39 PM

#16

The load against the deformed lugs is what bends the fork and pushes the 3rd pinion away from 4th. As soon as the two gears separate, the power flow continuity is interrupted, and the load disappears, leaving the tension on the fork pushing the two gears toward each other again. At first, they cannot re-engage because they are misaligned, lugs over lugs, but as soon as they rotate a third or quarter turn to the point where the lugs align with slots again, they drop back together to start the whole thing over again in a cycle. So, yes, the engine revs up as this happens, but only very briefly and thus very little. Changes in RPM are seldom really noticeable.

  • Spartan426

Posted February 16, 2012 - 09:46 PM

#17

Exactly what Gray said. I'm sorry i may have been adsadurateing, It revs up, But not VERY high, just abit so I let off the throttle. slows the rpm and load, allows the Dog teeth to re-engauge and yes I felt a complete loss of power to the engine as well. Think about it, the only thing transmitting your power from the combustion chamber to your rear tire, is your tranny gears. If it pops out of alingment, it will feel completely dead. And this happend to me either just being in third just putting around-ish and but morely when i was "on" the throttle much more noticeable when your accelerateing hard, and it slips out because of the high rpm.

Your welcome for the pics. glad i rememberd that I had those :bonk:


(P.s. I would never have chipped those gears my self, my Buddy i baught this bike from did ALOT of wheelies with it...by dumping the clutch in third :smirk: long story short over the time he owned it he chipped the gears. I'm just glad i caught it before anything drastic happend, when i baught the bike he told me what was going on w/ it so i examined the tranny in my complete engine rebuild found what was wrong and replaced my gear and the problem is solved :lol: )

(P.P.s I didn't replace my shift fork... I didn't think about it and my friend who was helping me build it, (vet racer been doing this for 45+ years) he said the forks looked good. And everything alinged perfectly when re-essmbled so I never thought about it... If the problem ever returns ill be sure to check that as well. Like Gray said, check both the gear dogs. AND the shift forks.)

Hope this helps, keep us informed on how the repair goes :lol:

  • Bansheeboy914

Posted February 21, 2012 - 06:02 PM

#18

Well, I had it out this weekend in Glamis. I didnt feel any feedback whatsoever when shifting into 4th and holding the shifter up, but I noticed that under a load (like when I was actually duning it) I would try to shift from 3rd, just barely click 4th, and go straight to 5th like I have been since the problem started, and it would mis-shift horribly in 4th. Looks like I'll be tearing it back down and splitting the cases this weekend.

  • Spartan426

Posted February 22, 2012 - 12:17 AM

#19

I'm surprised you took it out this weekend. Hope it was a good trip! never been to glamis, I want to some day. Let us know what you find out when you tear it apart! :bonk:

  • Bansheeboy914

Posted February 23, 2012 - 04:30 PM

#20

Are the gears model specific? Or could I use a set out of another bike? For example, an '03 yz450





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