06 yz 450 Missing when at steady throttle? Help???


41 replies to this topic
  • bsam450

Posted June 21, 2009 - 03:36 PM

#1

My 06 yz 450 is missing at steady throttle, it is strong under a load, but when I hold steady say down a fire road it will miss. Does any one have a suggestion? Valve adj? I put a new plug in and that was not it, Is it the plug cap? I re-packed the silencer and cleaned the end cap.

  • natethece

Posted June 21, 2009 - 03:57 PM

#2

it sounds like a jetting problem. try raising or lowering the needle, but try both to see if either helps.

  • bsam450

Posted June 21, 2009 - 05:41 PM

#3

This is a new bike to me, I have ridden it about 7-10 times, and all of a sudden this started happening, Do you still think it is the needle?? Why would it run great all the rest of the time then all of a sudden start missing???

  • Smokeslider

Posted June 21, 2009 - 06:11 PM

#4

could be a clogged jet. I'll assume that your air filter was clean? I would pop that carb off and clean that thing up.


Also, If it doesn't have a adjustable fuel screw, I would get one for it, it will save you a lot of headache.

  • bsam450

Posted June 22, 2009 - 05:31 AM

#5

My air cleaner was clean, If it was a clogged jet wouldn't it miss all the time? It doesn't miss under a load.

  • walent215

Posted June 22, 2009 - 05:44 AM

#6

My air cleaner was clean, If it was a clogged jet wouldn't it miss all the time? It doesn't miss under a load.


my 08 surged just the way your explaining,it didnt affect much other than cruising speed ,so i pretty much dismissed it because it ran great everywhere else.as someone mentione dearlier you may be able to tune it out with a needle adjustment.

  • davcon

Posted June 22, 2009 - 05:52 AM

#7

Two weeks ago my 08 did the same thing. Up until that point it ran flawlessly. The only difference was it was after a rain and the temp was cool and the humidity was up. Played with the air-fuel screw, no difference. Day before yesterday, rode the same area, back to its ol self. Outside temp was about 10 deg warmer and humidity low. That was my experience, hope it helps.

  • Auggie427s

Posted June 22, 2009 - 07:19 AM

#8

I have a 2000 YZ426f and I just noticed mine doing the same thing. I am newer to this bike. So I guess I'm also looking for an answer.

  • spark250

Posted June 22, 2009 - 07:32 AM

#9

I have the same bike, it tends to do that while at a constant RPM. But it's fine under acceleration or normal riding conditions.

  • Auggie427s

Posted June 22, 2009 - 07:41 AM

#10

Does Anyone Have An Answer To The Question?

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  • r1usn

Posted June 22, 2009 - 09:38 AM

#11

If it is surging at steady throttle. Disconnect the TPS. Pretty common thing on yamaha's. It works.

  • gdbarr1976

Posted June 22, 2009 - 10:01 AM

#12

My 08 did the same thing a few months ago when the temp was in the 30-40's. Now that it 80-100 it seems to have gone away which leads me to believe that I was a little lean in the mid range. As it warmed up it now seems to be jetted perfect. Of course the question is why was it lean. My guess is a thorough carb cleaning would have solved the problem but since it never was a issue in race mode I ignored it.

  • grayracer513

Posted June 22, 2009 - 10:50 AM

#13

My 08 did the same thing a few months ago when the temp was in the 30-40's. Now that it 80-100 it seems to have gone away which leads me to believe that I was a little lean in the mid range. As it warmed up it now seems to be jetted perfect. Of course the question is why was it lean?

Roughly each 11 ℉ changes the mixture enough to call for a 1% change in jet size. You're talking 5 to 6 times that, and YZF's come jetted on the lean side as it is. That's the difference between a 160 and a 168/170.

  • bsam450

Posted June 23, 2009 - 07:31 PM

#14

I unplugged the tps, and the miss went away. My buddy ex moto mech said this is not a wise thing to do, does anyone know if this will effect the mapping? By not having the tps plugged in what does the computer do? Does it assume it is at idle or full throttle position?

  • grayracer513

Posted June 23, 2009 - 07:48 PM

#15

It assumes full throttle, so it's safe enough, but you'll loose some of the part throttle crispness it should have. Test it thoroughly per the manual, and add a "sweep test". Read the resistance as you open the throttle slowly all the way, then close it. The resistance should change smoothly as you do this, with no sudden spikes, either up or down.

If it passes, be sure it's adjusted correctly and try jetting it correctly.

  • renodirtandsnow

Posted June 23, 2009 - 09:00 PM

#16

I have a 2006 YZ450F as well. Surges during steady throttle as well. But rips every where else....!!!! Except when it dies in corners.......( my first 4 stroke) :worthy:

  • r1usn

Posted June 24, 2009 - 03:51 AM

#17

I am not sure if you guys are familiar with Burned (Eddie Sisneros) But he is the one that reccomended for me to disconnect the tps on my 07 YZ450. He said it will have no effect on performance and from my experience he knows his stuff. Since i have disconnected mine i have seen no loss in throttle response or performance. If you do decide to disconnect it and leave it that way i recommend placing electrical tape over both the connectors and tucking them away in the frame.

  • grayracer513

Posted June 24, 2009 - 09:40 AM

#18

I am not sure if you guys are familiar with Burned (Eddie Sisneros) But he is the one that reccomended for me to disconnect the tps on my 07 YZ450. He said it will have no effect on performance and from my experience he knows his stuff. Since i have disconnected mine i have seen no loss in throttle response or performance. If you do decide to disconnect it and leave it that way i recommend placing electrical tape over both the connectors and tucking them away in the frame.

Its absence won't really be noticeable in most cases on an MX course, flat track, SM, etc., where there is little or no time spent at part throttle, but it can make a significant difference in fuel economy for a desert racer who spends long stretches at a 1/4 to 1/2 throttle "cruising" at speed, and that can make the difference between stretching one loop into two, or having to make the extra pit stop.

What it does is provide the CDI with information in the form of throttle position that it can use to calculate engine load by comparing it with the RPM signal from the trigger coil. The CDI, sensing a less than full throttle condition at higher speeds, advances the ignition farther than can be done at full throttle to help improve the combustion efficiency of the "thin" fuel charge that occurs under such conditions.

If the TPS is healthy, you should be able to jet around the stuttering. But, for many people, it won't matter too much if it's gone.

  • bsam450

Posted November 19, 2009 - 06:41 AM

#19

Try the tps, throttle positioning sensor, it is on the left side of the carb, it has an electrical connection, just un plug it, take it for a ride and see if that is your problem. I had the same problems you have. I unplugged mine and the problem went away.

  • tech24

Posted November 19, 2009 - 06:44 AM

#20

Could be possible build up or dirt in the carb. Tear down and cleaning may be worth a try. I am having similar but worse issues with mine and found a ton of dirt in carb but believe I have missed some. There are quite a few little passages in there that need to be open. Check your vent hoses for dirt too. I dont know how dirt gets in there but it does.

Sorry missed the last few posts about the tps...may be the problem





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