2004 YZ450F cutting out, please help


13 replies to this topic
  • twosixtwo

Posted January 31, 2005 - 07:37 PM

#1

It only does it in fourth gear and it cuts out really bad, I can redline it in third but as soon as I shift into fourth it starts to cut out, it doesnt slip, but loses power, then hooks up again, then loses power over and over:excuseme: :cry:

  • sirthumpalot

Posted January 31, 2005 - 08:00 PM

#2

The fact that it only does it in 4th gear makes me lean away from jetting or other similar issues. Are you sure the motor is actually cutting out? Does it feel like the chain is slipping on the sprockets type of feeling? If so, my guess would be gearbox.

  • twosixtwo

Posted January 31, 2005 - 08:38 PM

#3

Thats what it feels like, thanks for the input, there goes my tax return:thumbsdn: :cry:

Oh yeah does that mean I should replace the whole gear box

  • yamahazinger

Posted February 04, 2005 - 05:03 PM

#4

If i were you i would replace only the necessities unless you have the couple thousand it will take to replace the gearbox. :cry:

  • Frostbite

Posted February 04, 2005 - 05:31 PM

#5

If it is the engine quitting and if it only does it in fourth and cuts in and out it may be electrical. I assume that your 450 has a gear position sensor like the 400 and 426. It's under a black plastic cap the size of a silver dollar held on with 2 screws, (near the gearshift) and has wires coming out of it. Maybe you pinched a wire or maybe the problem is in the contacts under the cover. If you pop the cap off and look inside you'll see that the cap has a metal contact that corresponds with each gear and inside the hole in the case you'll see the end of the shift drum and a little tiny spring loaded bullet looking contact. As the shift drum turns I assume that the bullet connects the contact to ground since there are no wires in the shift drum itself.
If your bike only cuts out in fourth, then that's the only thing I can think of that tells your bike that it's in fourth. It can't be running out of fuel or jetting if it'll pull redline in all other gears. The only other things different about fourth gear is that the engine is lugging more and bike speed is higher. If you have some kind of ram air scoop the extra air pressure at high speed may be leaning out your carb.
It may also be something really wacky like a high speed vibration causing your carb float needle to jam up and run the float bowl low on fuel. It sometimes happens in modified sleds with solid mounted engines, vibration at a certain RPM will completely stop fuel flow and seize the 2 smoke. That would be way out there on you 450 though, I'd check the shift position sensor first.

  • twosixtwo

Posted February 04, 2005 - 06:18 PM

#6

Now the second problem that I encountered is when the bike is idling and I pull the clutch in, drop it into first it just dies. What the heck is wrong with my bike

  • Frostbite

Posted February 05, 2005 - 03:26 PM

#7

Now the second problem that I encountered is when the bike is idling and I pull the clutch in, drop it into first it just dies. What the heck is wrong with my bike


This is a tricky to diagnose without more info. Will the bike quit if you pop it into 2nd standing still with the clutch in or just 1st. It could be not enough play in your clutch cable, bike too lean and quits when it picks up the load of the clutch, or it could be your shift drum sensor.
If it is doing it in 4th and now 1st and no other gears I'd bet that somewhere you have a crossover(wires melted together) between your ignition or coil wire and the wires out of the shift drum sensor. Since the shift drum sensor connects each of the wires that correspond with the gear to ground, if there is connection with any of these wires and the ignition, it would send spark to ground just like your killswitch does.
If it started doing it in 4th and now is starting to do it in 1st I'd look for some chafing or melting wires. If there are other random problems in all gears it's probably something else.
Try a few things to check the gear sensor. Start the bike and either prop it on a stand to let the rear wheel spin or just hold the clutch in. Pop it in first, at idle and then revving a bit and see if it quits every time, just at idle, or intermittently. then do the same in 2nd, 3rd and 4th, sitting still. If it quits in 1st and 4th only that narrows the possibilities to electrical.
In this pic you can see the sensor cap just in front of the gear shift shaft. Trace the wire from the gear position sensor and make sure there are no burns or missing insulation. Here's what it looks like on the inside. You can see the round metal contacts, one for each gear, (mine is a 5 speed + the small on for neutral.)

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  • ncmountainman

Posted February 05, 2005 - 03:58 PM

#8

eliminate that whole circuit,thats what i did. still check the harness though. zip-ty makes a cover for the hole after you remove the switch. works fine without it :cry: hey frostbite did you ever do anymore testing after you wrapped the rad.? i did mine with glass cloth and aluminum tape. its gotta help some! man that rads only 3/8" above my powerbomb!

  • Frostbite

Posted February 07, 2005 - 06:21 AM

#9

eliminate that whole circuit,thats what i did. still check the harness though. zip-ty makes a cover for the hole after you remove the switch. works fine without it :cry: hey frostbite did you ever do anymore testing after you wrapped the rad.? i did mine with glass cloth and aluminum tape. its gotta help some! man that rads only 3/8" above my powerbomb!


I see you already saw the IR report, but there was no tape on the rad this time. It was a new used aluminum colored unit and wasn't bent towards the pipe the way the old black one was in the original test. The extra 1/4 inch made a big difference. The aluminum rad didn't heat up with proper clearance from the pipe, even without tape, but I am going to paint it and I will tape the bottom, or maybe I just won't paint the reservoir. Hey, that might be a better idea, just polish the bottom can and save the weight of the tape. I remember that your's is on a diet. :cry:
Interesting that removing the gear position sensor stuff doesn't affect performance. One less thing to worry about, especially that damn tiny contact and spring. I lost the spring during my rebuild and had to use a modified bic pen spring. Then I thought I lost a dowel and found the spring while I was looking for it. I think I'll scrap the whole deal. So you just pop on the zip ty cover and unplug the unit from the harness?

  • ncmountainman

Posted February 07, 2005 - 07:18 AM

#10

no issues so far and that was one of the first things to go,almost a year ago. $hitcan it. i'm sure someone is probly gonna say "oh my god yamaha put that there for a reason" pay no attention to them! :cry: like you said just one less thing to worry about..... :cry: i'm still considering wrapping the pipe now that i see some favorable responses on the "to wrap or not to wrap" post. ya,that aluminum tape sure will weight ya down,maybe titanium tape is in order? :cry:

  • Wyatt

Posted February 07, 2005 - 08:50 AM

#11

That sensor is there only to tell the CDI when the bike is in nuetral. It does not use all of the other contacts that are there. When the bike is in nuetral it has a lower rev limiter. If you remove the switch and install the aftermarket cover, all you do is remove the rev limiter in nuetral.

  • ncmountainman

Posted February 07, 2005 - 09:50 AM

#12

it still keeps the regular limit(eleventy-five00),i know because after letting my neighbor ride it (he rides a two stroke) he missed 2nd gear twice and i could hear it working(as i cringed) he hasn't ridden it since. :cry:

  • Frostbite

Posted February 07, 2005 - 11:11 AM

#13

it still keeps the regular limit(eleventy-five00),i know because after letting my neighbor ride it (he rides a two stroke) he missed 2nd gear twice and i could hear it working(as i cringed) he hasn't ridden it since. :cry:



I know the feeling. :cry:

  • eazrider

Posted February 07, 2005 - 11:23 AM

#14

My thoughts on the switch on the end of the shift drum are: I think Yamaha retards the ignition when the tranny is in neutral. If you start the bike in neutral and adjust the idle speed, and then drop it into gear, the idle speed increases, which is what happens if the timing is advanced the idle speed will increase as timing is increrased. Retarding it in neutral allows for easier starting, and smoother idling. Once underway, more performance is to be had from more advanced timing. I discovered this when adjusting my Rekluse clutch: when you're in neutral, idle is no problem, drop it into gear, the idle speed picks up, and the clutch starts to engage. The trick is to adjust the idle speed with the bike in gear. It idles a little slower in neutral, but it isn't a big deal. The other option is to unplug the wire from the shift cam, and the bike always thinks it is in gear and keeps the timing advanced.





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