2010-2012 YZ450F Loss of low to mid range power (timing)


15 replies to this topic
  • titanmx61

Posted October 03, 2012 - 09:36 AM

#1

A little history behind my issue. I bought a basket case 2011 YZ450 that needed rebuilt from the bottom up. In went the new Hot Rods crank kit and gaskets, Cosworth HCP, and new valves, along with a new cam chain. After my mechanic assembled everything, I did three sessions heat cycles to break in the bike. On the stand, the has a very slight lag in revs(compared side by side to a running YZF), and seems to run fine in the shop. Once off the stand, and put under load, the bike will bog from the low RPM's to mid, then clean out and accelerate like normal on top. It acts as if it were a loaded up 2-Stroke trying to clean out. We ran it for a good 10 minutes, and the problem still persists.

What we've done:
Swapped the fuel tank from the good YZF(no change)
Swapped the ECU from the good YZF(no change)
Did electrical diagnostic testing on the system which meets criteria in the service manual
Checked timing
Tried different maps
Pulled the injector looking for clogs


Today, they looked at timing once again. When the mechanic assembled the motor, he rebuilt it and timed it off the marks on the crank. At first they believed they got a bad crank that was off by a few degrees, but Hot Rods has had no other issues reported thus far. Is there something tricky that we need to be aware of when timing the 2010-2012 bikes that may be causing my issue? Could this be a bad stator? Fuel? HELP!

Thanks~

  • grayracer513

Posted October 03, 2012 - 11:05 AM

#2

Run a complete check on the TPS per the manual.

  • BBrown626

Posted October 03, 2012 - 07:18 PM

#3

check timing again? Verify TDC with a dial indicator, as we did with our 2-smokes.

  • titanmx61

Posted October 03, 2012 - 08:32 PM

#4

I think they are down to 3 last options before chasing wiring.

In the AM we will:

A. Swap the stator or....
B. Swap the TPS or....
C. Unplug the kill switch...


Today they checked timing with another YZ450, which looked exactly the same, and thanks to you Gray, they now know about the 23 degree advanced timing ATDC. I appreciate all the help on past threads as I hope we're getting the issue narrowed down. Any more ideas that we may be missing?

  • titanmx61

Posted October 06, 2012 - 03:23 PM

#5

So we checeked the last three things left; TPS, kill switch, and stator with no luck. Next the guys swapped the wiring harness, plugged the known working harness from a good bike onto it and it ran perfect. They then proceeded to plug the old harness back up, ran the bike, and it ran perfect. Soundsed like it could be a bad connector or possible wire problem inside the wrapped protector, but for safetys sake we ordered a completely new harness.

  • titanmx61

Posted October 15, 2012 - 09:43 AM

#6

Well....had a wiring harness sent from Japan, put it on the bike, but still no joy. The problem seemed to get better, but still not cured. Off idle, when I roll on the throttle, it spits and spiders, has no low end power until mid throttle, where it seems to come alive. I rode it side by side with a 2010 and there is no comparison. I lacks the off snap that the good running bike had. I'm running out of ideas. Could the decompression spring be wore out on the cam? Bent exhaust valve? A problem with the Throttle Body? We've swapped most everything else out. I'm getting fed up.

  • YZPaGuy

Posted October 16, 2012 - 04:52 PM

#7

Sounds like a short in the wiring. Maybe not at the harness but further away letting the stray voltage cause problems in the harness or burn out the harness quickly. I would trace all the wiring back and look for a slice or rub through. Put the other harness on your bike and the new one on the other bike and run it for while and see if the problem comes back. If it does then it is definetely stray voltage messing up the harness.

Al the above is not from a mechanic so take it with a grain of salt. I am an electrician though and have seen similar problems in complex electrical systems, just not with a dirt bike.

  • grayracer513

Posted October 17, 2012 - 06:57 AM

#8

Really? What would the source of this "stray voltage" be? That's completely unsupportable. A wiring harness can only have one of three faults:
  • One or more leads are routed incorrectly because of tampering or a manufacturing error
  • A short exists between two circuits or to ground
  • An open (or an intermittent open) circuit exists
Since replacing the harness did not correct the problem, the problem is not in the harness, and absent a complete short, which would prevent any part of the system from operating, the unit can't really produce enough current or voltage to "burn out the harness".

You say you did a complete check of the electrical system, but I see no specific mention of the ignition coil or the rectifier being tested. The coil is obvious enough. The rectifier is probably not at fault, but if it passes AC into the EFI/ignition system, it will play hell with the ECU. When checking the components for compliance with continuity specs, try tapping on them with a screwdriver handle or similar. I worked on a coil the other day that I could get the primary resistance to change by 300% just by rapping on the casing.

You also did not hear the 23 degree thing from me. I have never seen any indication that it's true, and there's no mention of it specifically in the manual. "ATDC" actually means AFTER top dead center, which would be retarded, not advanced. I suggest that you verify the proper keying of the flywheel, then check to see where in relation to true TDC the marks line up.

As to the auto decompression spring, if the spring were to become weak or break, the system would become inoperative, and you would have full compression at all speeds instead of having compression reduced at less than 700 RPM. That, you would notice very quickly.

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  • titanmx61

Posted October 18, 2012 - 12:20 PM

#9

Coil has been swapped. One of the last things the mechanic wants to do is swap the collant temperature sensor with a known good sensor. After that, a call to Yamaha is in order. We're running out of leads to chase.

  • grayracer513

Posted October 18, 2012 - 02:57 PM

#10

If you've tried alternate programs, have you also tried reading the data stream from the tuner as the engine runs and see if inputs and outputs are in range?

  • YZPaGuy

Posted October 20, 2012 - 09:54 AM

#11

So we checeked the last three things left; TPS, kill switch, and stator with no luck.[color=#FF0000] Next the guys swapped the wiring harness, plugged the known working harness from a good bike onto it and it ran perfect.[/color] They then proceeded to plug the old harness back up, ran the bike, and it ran perfect. Soundsed like it could be a bad connector or possible wire problem inside the wrapped protector, but for safetys sake we ordered a completely new harness.


[color=#FF0000]Well....had a wiring harness sent from Japan, put it on the bike, but still no joy. The problem seemed to get better, but still not cured.[/color] Off idle, when I roll on the throttle, it spits and spiders, has no low end power until mid throttle, where it seems to come alive. I rode it side by side with a 2010 and there is no comparison. I lacks the off snap that the good running bike had. I'm running out of ideas. Could the decompression spring be wore out on the cam? Bent exhaust valve? A problem with the Throttle Body? We've swapped most everything else out. I'm getting fed up.

Sounds like a short in the wiring. [color=#FF0000]Maybe not at the harness but further away letting the stray voltage cause problems in the harness or burn out the harness quickly. I would trace all the wiring back and look for a slice or rub through. [/color]Put the other harness on your bike and the new one on the other bike and run it for while and see if the problem comes back. If it does then it is definetely stray voltage messing up the harness.

Al the above is not from a mechanic so take it with a grain of salt. I [color=#FF0000]am an electrician though and have seen similar problems in complex electrical systems, just not with a dirt bike.[/color]

Really? What would the source of this "stray voltage" be? That's completely unsupportable. A wiring harness can only have one of three faults:

  • [color=#FF0000]One or more leads are routed incorrectly because of tampering or a manufacturing error[/color]
  • [color=#FF0000]A short exists between two circuits or to ground[/color]
  • [color=#FF0000]An open (or an intermittent open) circuit exists[/color]
[color=#008000]A wirng harnes and/or the wiring can have other problems then just the three stated above. Any current carrying conductor has an electromagnetic field that surrounds the wire unless it is a shielded wire, which no are on a dirt bike. This electrocmagnetic field can cause signal problems in other wires especially if the outer casing has been compromised, even more so if two wires have rubbed each other. They can also do so if they get wrapped around each other. The wires can be swapping currents enough to mess a electronic device up but not enough to blow a fuse, trip a circuit breaker, etc. We find this allot with generators that were installed with the start wires running with the power wires through conduit. The electromagnetic field causes a the start wires the send a enough current to randomly start the generator. We call this stray voltage. The reason I brought it up was the bike was a "basket case" so if when reassembling the bike they routed the wiring incorrectly too close to a heat source and/or wiring that carries a current it may be something to look into. Again, I'm not a mechanic, I'm an electrician and I seen these types of problems wreak havoc with systems. The harness could have a problem that causes a similar effect. If the plastic melts slightly the insulation value of the harness diminishes, this can also be true of a harness that was not manufactured correctly with walls that are too thin.[/color]
Since replacing the harness did not correct the problem, the problem is not in the harness, and absent a complete short, which would prevent any part of the system from operating, the unit can't really produce enough current or voltage to "burn out the harness".

[color=#008000]Above he states that a harness from a known working bike did correct the problem.[/color]

You say you did a complete check of the electrical system, but I see no specific mention of the ignition coil or the rectifier being tested. The coil is obvious enough. The rectifier is probably not at fault, but if it passes AC into the EFI/ignition system, it will play hell with the ECU. When checking the components for compliance with continuity specs, try tapping on them with a screwdriver handle or similar. I worked on a coil the other day that I could get the primary resistance to change by 300% just by rapping on the casing.

You also did not hear the 23 degree thing from me. I have never seen any indication that it's true, and there's no mention of it specifically in the manual. "ATDC" actually means AFTER top dead center, which would be retarded, not advanced. I suggest that you verify the proper keying of the flywheel, then check to see where in relation to true TDC the marks line up.

As to the auto decompression spring, if the spring were to become weak or break, the system would become inoperative, and you would have full compression at all speeds instead of having compression reduced at less than 700 RPM. That, you would notice very quickly.


Grey, nothing but respect to you. You are the man with bikes! Just trying to give him something to check. Whenever I post about motor stuff on here I make sure I add that I am not a mechanic. I would assume the bike has enough current running through it to cause a problem especially if some of the wires are routed in correctly but I don't know that for a fact. If the known working harness coorects the problem then try that one for a while and put the new one on the other bike, what can it hurt?

Edited by YZPaGuy, October 20, 2012 - 09:55 AM.


  • buchman

Posted October 29, 2012 - 07:02 AM

#12

Hi,

I have the same problem with my 2005 yz450f.

It started after I did a valve adjustment. I didn't touch anything else.

Did you solve your problem?

  • titanmx61

Posted October 30, 2012 - 02:27 PM

#13

The cam sprocket slipped slightly, which caused it to be out of time. After comparing them with Hot Cams you could clearly see a difference. Once we threw them in, got everything adjusted properly, it fired right up. The track test will be this weekend and I'll be able to report back then. Thanks again for everyones help!

  • mx369

Posted October 30, 2012 - 05:17 PM

#14

Try the reg/ rectifier? My 10 had similar probs. Took one from 12 and it runs great

  • buchman

Posted November 01, 2012 - 11:01 AM

#15

Which one of the sprocket cam slipped? the exhaust or the intake cam?

  • titanmx61

Posted November 01, 2012 - 07:39 PM

#16

Intake





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