What to try if TPS doesn't cure stutter...


11 replies to this topic
  • wrider

Posted April 23, 2007 - 06:55 PM

#1

I have a new (left over) '05 wr450. It suffers from the dreaded stutter at 50-55 mph on the road (1/8 to 1/4 throttle, low load). It is a very strong cutout, like the ignition is turning off and on.

My conditions are 0-4000 ft, and the weather right now is in the 70s.

I have disco'd the TPS sensor to no effect. This made me think that it's jetting, and likely too rich.

I have the JD kit, and have tried several different combinations. My experience tells me that if it is the jetting, then I am too rich on the needle. The wierd thing is that the richer I go, the softer the stutter seems to be (although it is still there). Leaner jetting results in more violent stutter.

settings I have tried:

165 main Red needle (5th clip position)
168 main Red needle (5th pos)
168 main Blue needle (2nd position)

zip ty fuel screw seems good at about 1.5 turns.

According to Indy's chart, the leaner end (top) of this list should be correct for my conditions (if I read his chart right). I can't say that I have seen significant difference in power between these jettings. Off-idle response is good, as is acceleration... but the stutter is fairly severe.

I have not tried any other jets (leak, etc).




I have read several posts that say "nothing seems to help". Has anyone tried throwing parts at it?

If it didn't have the coil in the cap, I would suspect an arc'ing high tension lead. Anyone tried replacing this?

How would I wire out the kill button?


Any help would be greatly appreciated, we are leaving on a trip to Moab the end of the week, and I expect there will be quite a bit of road work connecting the trails (hopefully I am wrong about this).

As many of you know, this is supremely frustrating!


Thanks,
-Ted

  • dominator426

Posted April 23, 2007 - 09:24 PM

#2

Is your WR uncorked at all or is it stock? Is the airbox lid still on? Try the 168 main with blue needle at position #3 and #4...

  • krissi

Posted April 24, 2007 - 12:53 AM

#3

hi i have the same problem . stutter will only go if i disconect the TPS sensor.
now the TPS is sett at 0,72 volts
main 170
pilot 50
5 clip on original nedle
fuel screw about 2 turns.
all mots donne
My conditions are 0-1000 ft. temp 53

Kris in iceland

  • wrider

Posted April 24, 2007 - 06:31 AM

#4

My other mods are:

- airbox snorkel removed, top opening enlarged, sides still intact.

- PMB silent insert

- grey wire disco'd

- wr timing

  • wrider

Posted April 24, 2007 - 06:38 AM

#5

hmmm. going to a 168 main and blue needle at position 3 or 4 would be richer.

Could stutter be caused by being too lean? I will try it.

  • GCannon

Posted April 24, 2007 - 08:27 AM

#6

[quote name='wrider']I have a new (left over) '05 wr450. It suffers from the dreaded stutter at 50-55 mph on the road (1/8 to 1/4 throttle, low load). It is a very strong cutout, like the ignition is turning off and on.

My conditions are 0-4000 ft, and the weather right now is in the 70s.

I have disco'd the TPS sensor to no effect. This made me think that it's jetting, and likely too rich.

I have the JD kit, and have tried several different combinations. My experience tells me that if it is the jetting, then I am too rich on the needle. The wierd thing is that the richer I go, the softer the stutter seems to be (although it is still there). Leaner jetting results in more violent stutter.

Stutter and Surge is a "LEAN" condition you seam to be on the right track with your testing however you may be tunning in the wrong direction.
A "Rich" condition is generally a smother flatter feeling low on power

Try raising the needle one or two slots or increase the main one size and then adjust the needle as needed.

This is the RPM and Load area where the factory may do most of the sound and emisson testing and is less concerned with driveablity than passing tests.

Constant throttle conditions do not have an overly rich accelerator pump squirt to cover the existing lean condition which you would have under normal dirt riding conditions (constanly transitioning throttle)

Go richer in this area. Remeber if you change the accelerator pump squirt it will affect the mixture in this area. if you change the main jet that will affect what happens with the needle. Alittle richer on the fuel screw may also help transition just off idle.

You are already pretty close to working this out. Good luck:thumbsup:

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  • WGP

Posted April 24, 2007 - 09:02 AM

#7

A great starting place should be:

168 Main
48 Pilot
40 Leak (very important!)

I have found if you ride at any altitude, the Blue needle causes a huge stutter at low rpms, so if your going to ride in Moab put in Red #5

You say ( 0-4000) probably need the red....

  • WR450RICKO

Posted April 24, 2007 - 03:22 PM

#8

4th positon on the needle using the stock main jet, 2 to 2 1/2 turns out on the screw
works for me

  • wrider

Posted April 24, 2007 - 04:05 PM

#9

my stock needle doesn't have different clip positions, so are you talking about one of the JD needles, or an older WR needle?

This afternoon I started with
----------------------------
165 main, red needle, 5th position

Stutter was quite strong. I changed the main jet to a 170, and the stutter is less frequent and less strong. I am thinking about changing to the blue needle next, maybe 4th position. This will richen things up (probably way too much) but if the stutter is gone I can always lean it back out.

I told my local yamaha parts guy about what I was feeling and he said "yea, my 250 does that, you can't get rid of it". He let me ride it and although I felt what he was talking about, it was very mild compared to what I am chasing (mine bucks).

BTW, thanks for the input!

  • Humunn

Posted April 25, 2007 - 05:23 AM

#10

I had the same problem on my 07. From what I've read disconnecting the TPS may resolve the stutter but leads to other problems. Your solution is in the jetting. I ride between 3000 and 7000 feet and I had the shop install the following based on recommendations from Dirt Bike mag:

175 main
JYTR needle in 4th position
50 pilot
45 leak
110 air

Prior to these changes it had

152 main
48 pilot
70 leak
60 air
NCV needle in 4th position

I was concerned about running too rich on the new settings and at my elevation but these bikes come extremely lean from the factory. Almost all the stutter is gone. If I'm on pavement I sometimes notice a slight "tap" but not enough to richen it any further.

Don't mess with the TPS. It is in the jetting.

Greg

  • WR450RICKO

Posted April 25, 2007 - 01:37 PM

#11

I bought the GYTR AIS removal kit and installed everything per the instructions. Bike ran great. Took it in for the initial valve adjustment and had an adjustable air screw put in the carb. The MX shop put it on the dyno and turned the screw out 2 3/4 to get it to run most efficient. It rips right now. Smooth hard excelleration with no popping on decel. I ride from Sea Level to 5000 with very little change in performance.

  • wrider

Posted April 27, 2007 - 05:54 AM

#12

update:

I installed the blue needle and had no positive result... so I started looking at it like an electrical problem.

I pulled every electrical connector I could find and filled the female ends with dielectric grease. I also did this to the spark plug cap, while changing the spark plug. Guess what? the plug was completely sooted up, I take this to indicate that it was too rich. So at this time I changed from a 170 main to a 168 and went back to the red needle (5th), TPS disco'd.

Took it out for a ride and the major stumble was gone. There is still some hunting around when at 55mph, it is not rock steady but not bucking. Either the dielectric grease or the new plug made a difference.

I then reconnected the TPS and the bike started bucking. I then adjusted the TPS to .77 volts and the bucking remained. On the side of the road I rotated the TPS to something less than .77 volts (voltmeter was at home) and it did not help. Disconnecting the TPS (again) got rid of the bucking. Now it seems my bike is acting "normal"!

I pulled it back apart to put in the stock spring under the fuel mixture screw (the one that came with the zipty was too strong, very hard to turn) and checked the plug. This was the new plug and it was sooty black again, so I went ahead and changed the main to a 165. A short test run did not buck, so I changed the oil and am about to load it up on the truck for the long drive to Utah.

Thanks for the help, I think that it is a multifaceted problem. Hopefully it will not buck, and the jetting will be close enough in Moab that I don't have to muck with it.

I think I will get it on a dyno when I get back, to try to get some definitive answers on where the jetting is.


I'm outta here!




 
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